Reaction to form amino acid $$\ce{CH2=CH-CH=O -&gt;[CH3SH][(1,4 addition)] Product (P_1) -&gt;[(i) NaCN][(ii) NH3\\(iii) H3O+] Q_1}$$
Correct statement regarding $\ce{Q_1}?$

$\ce{Q_1}$ is essential amino acid
$\ce{Q_1}$ is acidic amino acid
$\ce{Q_1}$ is nonessential amino acid
$\ce{Q_1}$ on Lassign test gives prussian blue colour with $\ce{FeSO4}$ and $\ce{FeCl3}$ solution


By 1,4 addition (as mentioned in question) carbon-3 (taking carbon as carbon-1 of aldehyde group) will have $\ce{SCH3}$ added to it and oxygen must have $\ce{H}$ added to it.
After $\text{P}_1$ is formed, it can again tautomerize from an alcohol to an aldehyde.
The $\ce{^-CN}$ can now attack the aldehyde. Looking at the answer we can ay that the product must be an amino acid and so the $\ce{NH3}$ group and $\ce{^-CN}$ must be present on same carbon because then the $\ce{^-CN}$ will hydrolyze to give a $\ce{-COOH}$ group.
But how is $\ce{NH3}$ supposed to attack a carbon having $\ce{^-CN}$ and a hydroxyl group. Can we make the alcohol a leaving group somehow?
Or is the number of carbons in chain 1 less than what it should be? What should be the correct answer and approach for this problem?
The starting compound is an organic compound known as acrolein. $\ce{CH2=CH-CH=O}$
Now your first reaction would be:
$$\ce{CH2=CH-CH=O -&gt;[CH3SH][1,4 addition]CH3-S-CH2-CH=CH-OH} $$
Now, this compound tautomerizes to form methional
$$\ce{CH3-S-CH2-CH=CH-OH &lt;-&gt; CH3-S-CH2-CH2-CH=O}$$
Now, the second step in your reaction is a named reaction known as Strecker Amino Acid Synthesis. This converts an methional (in this case) into methionine.

Now, onto the question at hand, it asks about certain properties of methionine. Methionine is an essential amino acid. So A is correct. Since methionine doesn't have any extra acid or base groups, it is neutral.
As for the Lassaigne Test, if the compound had only nitrogen, it would have shown a prussian blue color. However since there is sulphur as well, it shows a violet colouration. So, the answer is A.