In the following sequence of reactions, ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{\mathrm{P}+{\mathrm{I}}_2}{\to }\mathrm{A}$$\underset{ether}{\overset{Mg}{\to }}B$$\underset{ }{\overset{HCHO}{\to }}$$C\stackrel{ }{\stackrel{H_2{O}^{+}}{\to } D}$ the compound D is

Given data : It is given to identify  compound D in the following chemical reaction. 

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{\mathrm{P}+{\mathrm{I}}_2}{\to }\mathrm{A}$$\underset{ether}{\overset{Mg}{\to }}B$$\underset{ }{\overset{HCHO}{\to }}$$C\stackrel{ }{\stackrel{H_2{O}^{+}}{\to } D}$ 

Explanation 
When ethanol is treated with a phosphorus-iodine mixture, ethyl iodide ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{I} \left(\mathrm{A}\right)$ is formed.

When compound A reacts with Mg metal in ether, it produces ethyl magnesium iodide ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{MgI} \left(B\right)$.

When compound B reacts with formaldehyde, it forms compound  ${\mathrm{CH}}_3{\mathrm{CH}}_2-{\mathrm{CH}}_2-\text{ OMgX (C)}$, which when hydrolyzed yields n propyl alcohol ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH} \left(D\right)$.

n-propyl alcohol is the compound D.

The chemical reaction is as follows.

Hence, the correct option (D). n-propyl alcohol.