# In which of the following reactions, $MgO$ is not formed?

$\begin {array} {1 1} (a)\;Mg+CO_2 \longrightarrow & \quad (b)\;Mg+dil. HNO_3 \longrightarrow \\ (c)\;Mg+NO_2 \underrightarrow {\Delta} & \quad (d)\;Mg+B_2O_3 \longrightarrow \end {array}$

Ans: $(B)\;Mg+dil. HNO_3 \longrightarrow$
$4 Mg+dil. 10 HNO_3 \longrightarrow 4Mg (NO_3)_2 + NH4NO_3 + 3H_2O$