Concept:
Sodium borohydride reacts with iodine to produce diborane. Diborane further decomposes to give hydrogen and boron hydrides. The reaction ultimately yields a solid and a mixture of gases including a colourless toxic gas.
Step 1: Consider the reaction of \(NaBH_4\) with \(I_2\).
\[
2NaBH_4 + I_2
\rightarrow
B_2H_6 + 2NaI + H_2
\]
Here,
\[
NaI
\]
is a solid.
Step 2: Identify the gaseous products.
The gases formed are
\[
B_2H_6
\]
and
\[
H_2.
\]
Diborane,
\[
B_2H_6,
\]
is a colourless toxic gas.
Step 3: Match with the given condition.
The reaction produces:
• a solid (\(NaI\))
• a mixture of two gases (\(B_2H_6\) and \(H_2\))
• one gas is colourless and toxic (\(B_2H_6\))
Therefore,
\[
\boxed{X=NaBH_4,\qquad Y=I_2}
\]
\[
\boxed{\text{Answer = (B)}}
\]