$C{H}_{3}C{H}_{2}Cl\underset{C_2{H}_{6}OH}{\overset{NaCN}{\to }}$A (major) + B (minor). Covalency of carbon and N in the  ‘B’ is

Ionic cyanides like KCN & NaCN with RX give RCN as major product & RNC as minor product 

$C{H}_3-C{H}_2-\underset{\left(A\right)}{C}\equiv N\left(\text{major}\right)\&C{H}_3-C{H}_2-\underset{\left(B\right)}{N}\underset{¯}{\underset{¯}{\to }}C\left(\text{minor}\right)$

functional group is $-C\equiv N$

Covalency of ‘C’ is 4

Covalency of ‘N’ is 3

In $-C_2{H}_5 group$ of $C_2{H}_{5}NC$

covalency of carbon is 4 but in $-N\underset{¯}{\underset{¯}{\to C}}$

Covalency of ‘N’ is 4

Covalency of ‘C’ is 3