Referring to the following reactions the missing products A, B, C, and D respectively are
$NH_4Cl (aq) + NaNO_2 (aq) \rightarrow$ [A] $+ H_2O (l) + NaCl (aq)$
$(NH_4)_2Cr_2O_7 \xrightarrow{\Delta}$ [B] $+ H_2O (l) + Cr_2O_3 (s)$
$Cu + HNO_3$ (dilute) $\rightarrow Cu(NO_3)_2 +$ [C] $+ H_2O (l)$
$Cu + HNO_3$ (concentrate) $\rightarrow Cu(NO_3)_2 +$ [D] $+ H_2O (l)$