Which of the following hybridisation has the highest percentage of $s-$character?

$H - C \equiv C - C \equiv C - CH_3$
Compare the bond lengths $a$ and $b$.

Consider the following reaction: $MX_4 + X'_2 \to MX_4X'_2$. If the atomic number of $M$ is $52$ and $X$ and $X'$ are halogens and $X'$ is more electronegative than $X$. Then choose the correct statement regarding the given information.

$A + 2Cl^{-} \rightarrow B$
Where $A$ is $PCl_4^+$ and $B$ is $PCl_6^-$.
Which of the following statements is $INCORRECT$:
$(I)$ From $B$ to $A$,the number of $d$-orbitals involved in hybridization increases.
$(II)$ From $A$ to $B$,the percentage of $p$-character in the $P-Cl$ bond increases.
$(III)$ The number of covalent bonds in $A$ and $B$ are the same.
$(IV)$ $B$ is a product of Lewis acid-base interaction,which is associated with super-octet molecules only.

Which of the following will be octahedral?

In the process $XH_3 + H^{+} \to XH_4^+ (X = N, P, As, Sb)$,the maximum increase in bond angle occurs in the case of: