JEE Chemistry 2023 Question with Solution

Given:

• Assertion ($A$): The first ionization enthalpy of $3d$ series elements is more than that of group $2$ metals.
• Reason ($R$): In $3d$ series of elements, successive filling of $d$-orbitals takes place.

Find: Which option correctly describes the truth values of $A$ and $R$.

The solution states that from Sc to Mn, ionization energy is less than that of Mg.

For $3d$ series, the listed ionization enthalpies are:

• Sc: $631 \, \text{kJ mol}^{-1}$
• Ti: $656 \, \text{kJ mol}^{-1}$
• V: $650 \, \text{kJ mol}^{-1}$
• Cr: $653 \, \text{kJ mol}^{-1}$
• Mn: $717 \, \text{kJ mol}^{-1}$
• Fe: $762 \, \text{kJ mol}^{-1}$
• Co: $758 \, \text{kJ mol}^{-1}$
• Ni: $736 \, \text{kJ mol}^{-1}$
• Cu: $745 \, \text{kJ mol}^{-1}$
• Zn: $906 \, \text{kJ mol}^{-1}$

For group $2$, the listed ionization enthalpies are:

• Be: $631 \, \text{kJ mol}^{-1}$
• Mg: $656 \, \text{kJ mol}^{-1}$
• Ca: $650 \, \text{kJ mol}^{-1}$
• Sr: $653 \, \text{kJ mol}^{-1}$
• Ba: $717 \, \text{kJ mol}^{-1}$
• Ra: $762 \, \text{kJ mol}^{-1}$

Thus, the assertion that the first ionization enthalpy of $3d$ series elements is more than that of group $2$ metals is false.

The reason is true because in the $3d$ series, successive filling of $d$-orbitals does take place.

Therefore, the correct option is C: ($A$) is false but ($R$) is true.

Given: Two statements, one assertion and one reason.

Find: Whether the assertion and reason are true or false.

The solution compares first ionization enthalpy data directly. The statement in the solution says:

From Sc to Mn, ionization energy is less than that of Mg.

So the claim that all $3d$ series elements have first ionization enthalpy greater than group $2$ metals is not valid. Hence Assertion (A) is false.

The Reason (R) says that in the $3d$ series, successive filling of $d$-orbitals takes place. This is a correct electronic-configuration fact, so R is true.

Therefore, the final conclusion is that A is false but R is true, so the correct option is C.