Of the following,the most acidic is

In which of the following is $NH_3$ $NOT$ used?

Which nitrogen trihalide is the least basic?

Consider the following reaction:
$A +$ alkali $\rightarrow B$ (Major Product)
If $B$ is an oxoacid of phosphorus with no $P-H$ bond,then $A$ is ..... .

$Pb + \text{dil. } HNO_3 \xrightarrow{\text{Warm}} P + Q \uparrow + H_2O$
The incorrect statement for $Q$ is:

In the following reaction,assign the correct option for the underlined atom in the product of complete hydrolysis at $R.T.$:
$\underline{N}_2O_3 + H_2O \longrightarrow 2HNO_2$