Assertion(A): In the Lassaigne’s test for halogens, Lassaigne’s extract is boiled  with conc. $HN{O}_3$  before testing for halogen. 
Reason (R) : Conc.  ${\text{HNO}}_{\text{3}}$ decomposes  NaCN to HCN and ${\text{Na}}_{\text{2}}\text{S}$  to  ${\text{H}}_{\text{2}}\text{S}$ and thus prevents their interference in the reaction