diff --git a/education/chemistry/1.html b/education/chemistry/1.html
index f11372e..dee43bf 100644
--- a/education/chemistry/1.html
+++ b/education/chemistry/1.html
@@ -2,7 +2,7 @@
 title: 1
 description: 
 published: true
-date: 2026-02-11T15:38:17.754Z
+date: 2026-02-11T15:42:38.277Z
 tags: 
 editor: ckeditor
 dateCreated: 2026-02-11T14:58:54.870Z
@@ -40,14 +40,13 @@ dateCreated: 2026-02-11T14:58:54.870Z
   </table>
 </figure>
 <p>&nbsp;</p>
+<h3><span style="font-family:Arial, Helvetica, sans-serif;">Element</span></h3>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Protons = Electrons ⇒ Atom. Neutral.</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Protons ≠ Electrons ⇒ Ion. Charged.</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Electrons are surrounding the nucleus, consisting of protons and neutrons.</span></p>
 <p>&nbsp;</p>
-<h3><span style="font-family:Arial, Helvetica, sans-serif;">Element</span></h3>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Mass number are the number of protons and neutrons in the nucleus.</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Atomic number are the number of protons in nucleus.</span></p>
-<p>&nbsp;</p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">For example, <sup>4</sup><sub>2</sub>He, where mass number is written on top left, and atomic number on bottom left.</span></p>
 <p>&nbsp;</p>
 <h3><span style="font-family:Arial, Helvetica, sans-serif;">Periodic Table</span></h3>
@@ -130,8 +129,8 @@ dateCreated: 2026-02-11T14:58:54.870Z
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">g</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">9</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">18</span></td>
-        <td style="text-align:center;">&nbsp;</td>
-        <td style="text-align:center;">&nbsp;</td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
     </tbody>
   </table>
@@ -175,9 +174,9 @@ dateCreated: 2026-02-11T14:58:54.870Z
     <tbody>
       <tr>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⇡⇣</span></td>
-        <td style="text-align:center;width:60px;">&nbsp;</td>
+        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⇡⇣</span></td>
-        <td style="text-align:center;width:60px;">&nbsp;</td>
+        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⇡⇣</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⇡⇣</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⇡⇣</span></td>
@@ -190,13 +189,13 @@ dateCreated: 2026-02-11T14:58:54.870Z
       </tr>
       <tr>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">1s</span></td>
-        <td style="text-align:center;">&nbsp;</td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">2s</span></td>
-        <td style="text-align:center;">&nbsp;</td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;" colspan="3"><span style="font-family:Arial, Helvetica, sans-serif;">2p</span></td>
-        <td style="text-align:center;">&nbsp;</td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">3s</span></td>
-        <td style="text-align:center;">&nbsp;</td>
+        <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;" colspan="3"><span style="font-family:Arial, Helvetica, sans-serif;">3p</span></td>
       </tr>
     </tbody>
@@ -205,27 +204,27 @@ dateCreated: 2026-02-11T14:58:54.870Z
 <p>&nbsp;</p>
 <h3><span style="font-family:Arial, Helvetica, sans-serif;">Aufbau principle</span></h3>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">The lowest energy subshell or orbital will be filled first</span></p>
-<p><span style="font-family:Arial, Helvetica, sans-serif;">1s &lt; 2s &lt; 2p &lt; 3s &lt; 3p &lt; 4s &lt; 3d</span><br>&nbsp;</p>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">1s &lt; 2s &lt; 2p &lt; 3s &lt; 3p &lt; 4s &lt; 3d</span><br><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Imagine drawing a line from right to left.</span></p>
-<p><span style="font-family:Arial, Helvetica, sans-serif;">You should be able to find out that 4s subshell has a lower energy than 3d subshell this way.</span><br>&nbsp;</p>
+<p><span style="font-family:Arial, Helvetica, sans-serif;">You should be able to find out that 4s subshell has a lower energy than 3d subshell this way.</span><br><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></p>
 <figure class="table">
   <table>
     <tbody>
       <tr>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>n</strong></span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>1</strong></span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
@@ -235,67 +234,67 @@ dateCreated: 2026-02-11T14:58:54.870Z
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>1</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">1s</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>2</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>3</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>2</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">2s</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">2p&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>4</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>5</strong></span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
-        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
-        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>3</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">3s</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">3p&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">3d</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>6</strong></span></td>
@@ -303,13 +302,13 @@ dateCreated: 2026-02-11T14:58:54.870Z
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>7</strong></span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
         <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
@@ -317,61 +316,61 @@ dateCreated: 2026-02-11T14:58:54.870Z
       </tr>
       <tr>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>4</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">4s</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">4p&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">4d</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">4f</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>8</strong></span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;"><strong>5</strong></span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">5s</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">5p&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">5d</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;"><span style="font-family:Arial, Helvetica, sans-serif;">5f</span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
       <tr>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
         <td style="text-align:center;width:60px;"><span style="font-family:Arial, Helvetica, sans-serif;">⁄&nbsp;</span></td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
-        <td>&nbsp;</td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
+        <td><span style="font-family:Arial, Helvetica, sans-serif;">&nbsp;</span></td>
       </tr>
     </tbody>
   </table>
 </figure>
 <p>&nbsp;</p>
-<h3><span style="font-family:Arial, Helvetica, sans-serif;">Pauli's Exclusion principle</span></h3>
+<h3><span style="font-family:Arial, Helvetica, sans-serif;">Pauli's exclusion principle</span></h3>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">Each orbital can be occupied by no more than 2 electrons.</span></p>
 <p><span style="font-family:Arial, Helvetica, sans-serif;">If 2 electrons occupy the same orbital, they must have opposite spins.</span></p>
 <p>&nbsp;</p>