Consider the following reactions (not balanced):
$BF_3 + NaH \xrightarrow{450 \ K} X + NaF$
$X + H_2O \longrightarrow Y + H_2 \uparrow$
The correct statements about $X$ and $Y$ are:
$I$. $X$ is an electron-deficient molecule
$II$. In $X$, $B-B$ bond is present
$III$. $Y$ is a weak tribasic acid
$IV$. $Y$ acts as a Lewis acid

• A
  $I$ and $IV$
• B
  $II$ and $III$
• C
  $II$ and $IV$
• D
  $I$ and $III$