JEE Chemistry 2025 Question with Solution

Given: First ionisation enthalpy values of group $15$ elements are listed in the options.

Find: The correct value for the element that is a main component of the apatite family.

Apatite minerals are mainly phosphate minerals, so the key element involved is phosphorus.

Phosphorus belongs to group $15$, and its first ionisation enthalpy is

$$1012 \, \text{kJ mol}^{-1}$$

Hence, the required value is $1012 \, \text{kJ mol}^{-1}$.

Therefore, the correct option is A.

Given: We need to identify the first ionisation enthalpy of the element that is the main component of the apatite family.

Find: Which option matches that value.

Apatite is a group of phosphate minerals with general formula

$$\text{Ca}_5(\text{PO}_4)_3(\text{F, Cl, OH})$$

So, the key element is phosphorus because it occurs in the phosphate ion

$$\text{PO}_4^{3-}$$

The first ionisation enthalpy trend down group $15$ decreases approximately as:

• $\text{N} = 1402 \, \text{kJ mol}^{-1}$
• $\text{P} = 1012 \, \text{kJ mol}^{-1}$
• $\text{As} = 947 \, \text{kJ mol}^{-1}$
• $\text{Sb} = 834 \, \text{kJ mol}^{-1}$

Thus, for phosphorus, the correct value is $1012 \, \text{kJ mol}^{-1}$.

Therefore, the correct option is A.