What is the reason behind gallium having less atomic radius than aluminium?

Given below are two statements: one is labelled as Assertion $\mathrm{A}$ and the other is labelled as Reason $\mathrm{R}$.

Assertion $\mathrm{A}:$ In $\mathrm{T}l{\mathrm{I}}_3,$ isomorphous to ${\mathrm{CsI}}_3$, the metal is present in $+1$ oxidation state.

Reason $\mathrm{R}:$ $\mathrm{T}l$ metal has fourteen $\mathrm{f}$ electrons in its electronic configuration.

In the light of the above statements, choose the most appropriate answer from the options given below:

Given below are two statements:
Statement $\mathrm{I}:$ Colourless cupric metaborate is reduced to cuprous metaborate in a luminous flame.

Statement $\mathrm{II}:$ Cuprous metaborate is obtained by heating boric anhydride and copper sulphate in a non-luminous flame.

In the light of the above statements, choose the most appropriate answer from the options given below.

Given below are two statements:

Statement I: The decrease in first ionization enthalpy from $\mathrm{B}$ to $\mathrm{Al}$ is much larger than that from $\mathrm{Al}$ to $\mathrm{Ga}$.

Statement II: The d orbitals in $\mathrm{Ga}$ are completely filled.

In the light of the above statements, choose the most appropriate answer from the options given below