Why is it necessary to avoid even traces of moisture during the use of a Grignard reagent?

$(CH_3)_3CBr + KOH (aq.) \to (CH_3)_3COH + KBr$. The above reaction is:

Which of the following undergoes $S_{N^{1}}$ reaction?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$ :
Assertion $(A)$ : $S_N2$ reaction of $C_6H_5CH_2Br$ occurs more readily than the $S_N2$ reaction of $CH_3CH_2Br$.
Reason $(R)$ : The partially bonded unhybridized $p$-orbital that develops in the trigonal bipyramidal transition state is stabilized by conjugation with the phenyl ring.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following does not form a Grignard reagent?

$CH_3Br + Nu^{-} \rightarrow CH_3-Nu + Br^{-}$
The decreasing order of the rate of the above reaction with nucleophiles $(Nu^{-})$ $A$ to $D$ is
$[Nu^{-} = (A) \, PhO^{-}, (B) \, AcO^{-}, (C) \, HO^{-}, (D) \, CH_3O^{-}]$