Given below are two statements : Statement I : The decrease in first ionisation enthalpy from B to A

Question

Given below are two statements : Statement I : The decrease in first ionisation enthalpy from B to Al is much larger than that from Al to Ga .\ Statement II : The $d$-orbitals in Ga are completely filled. In the light of the above statements, choose the most appropriate answer from the options given below :\

Professor PC Thomas Classes · Answer

(a) : The decrease in first ionisation enthalpy from B to Al is associated with increase in size. The discontinuity between Al and Ga is due to low screening effect of $d$-electrons. 
$\begin{array}{lccc}
 & 	ext{B} & 	ext{Al} & 	ext{Ga} \
1^{	ext{st}} 	ext{ Ionisation enthalpy (kJ/mol)} & 801 & 577 & 579 \
\end{array}$
 In $\mathrm{Ga}:[\mathrm{Ar}] 3 d^{10} 4 s^{2} 4 p^{1}, d$-orbitals in Ga are completely filled.\