$A$ soft heavy metal melts at $30\ ^oC$ and is used in making heat-sensitive thermometers. The metal is:

$NH_3 + O_2 \xrightarrow[500 \ K]{Pt} W + H_2O$
$W + O_2 \rightleftharpoons X$
$X + H_2O \rightleftharpoons Y + W$
Which of the following statements is correct?

Nitrogen dioxide $(NO_2)$ reacts with water to give:

Reaction of ammonia with excess $Cl_2$ gives:

Which of the following tendencies remains unchanged on going down in the nitrogen family (Group-$15$)?

Of the following,the most acidic is