What is the chemical formula for urea?

Study the flow chart given and give balanced equations to represent the reactions A, B and C.

Name the gas evolved when the following mixtures are heated:

Ammonium chloride and slaked lime.

Consider the following reactions:

$\left(\mathrm{i}\right)$ ${\mathrm{NH}}_4\mathrm{Cl} \underset{∆}{\overset{\mathrm{NaOH}}{\to }}$ product (containing nitrogen).
$\left(\mathrm{ii}\right)$ ${PH}_4\mathrm{I}\underset{∆}{\overset{\mathrm{NaOH}}{\to }}$ product (containing phosphorus).
$\left(\mathrm{iii}\right)$ ${\mathrm{P}}_4\underset{∆}{\overset{\mathrm{NaOH}}{\to }}$ product (containing phosphorous in negative oxidation state).

The order of change in bond angle (for reactant $\to$ specified product) is:

In which substance does nitrogen exhibit the lowest oxidation state?