The element which is not common between the compounds called baking soda and soda ash is :

Question

Accepted Answer

The question asks which element is not common between the compounds known as baking soda and soda ash. The correct answer is Option 2: Hydrogen.

1. **Explanation for Option 2 (Hydrogen):**
   - Baking soda is chemically known as sodium bicarbonate (NaHCO₃). It contains the elements sodium (Na), hydrogen (H), carbon (C), and oxygen (O).
   - Soda ash is chemically known as sodium carbonate (Na₂CO₃). It contains the elements sodium (Na), carbon (C), and oxygen (O).
   - The key difference between these two compounds is the presence of hydrogen. Baking soda contains hydrogen, whereas soda ash does not. Therefore, hydrogen is the element that is not common between the two compounds, making Option 2 the correct answer.

2. **Explanation for why the other options are incorrect:**
   - **Option 1 (Oxygen):** Both baking soda (NaHCO₃) and soda ash (Na₂CO₃) contain oxygen. In fact, both compounds have three oxygen atoms in their chemical formulas. Therefore, oxygen is a common element in both compounds, making Option 1 incorrect.
   - **Option 3 (Sodium):** Sodium is present in both baking soda and soda ash. Baking soda has one sodium atom (NaHCO₃), and soda ash has two sodium atoms (Na₂CO₃). Since sodium is common to both compounds, Option 3 is incorrect.
   - **Option 4 (Carbon):** Carbon is also present in both compounds. Baking soda contains one carbon atom (NaHCO₃), and soda ash contains one carbon atom (Na₂CO₃). As carbon is a shared element in both compounds, Option 4 is incorrect.

In conclusion, hydrogen is the only element that is present in baking soda but not in soda ash, which justifies why Option 2 is the correct answer.