Question

Assertion:
Phosphate gives a yellow crystalline precipitate upon addition of nitric acid and ammonium molybdate.
Reason:
Phosphate show no change with ${H_2}S{O_4}$
A. Both assertion and reason are correct and the reason is the correct explanation of assertion.
B. Both assertion and reason are correct but the reason is not the correct explanation of assertion.
C. An assertion is correct but the reason is not correct.
D. Both assertion and reason are not correct.

Answer 1

The test used for finding the presence of any compound is known as qualitative compound. Covalent compounds can be identified by using various physical properties such as boiling point whereas for the case of ionic compounds we need to use the chemical properties of a compound to identify the same

Complete step by step answer:
The different tests used to find the phosphate ions in the solution are classified as phosphate tests and there are different qualitative and quantitative phosphate tests. In this case the quantitative tests help us find the amount of phosphate available in the solution where the qualitative test helps us determine the presence of phosphate ions.
The assertion given is the statement is a part of the qualitative method used to determine the presence of phosphate ions. In this case, when the Conc. Nitric acid ($HN{O_3}$) is added to a solution containing phosphate ions ($P{O_4}^{3 - }$), followed by addition of excess of ammonium molybdate (${(N{H_4})_2}Mo{O_2}$), we can see yellow precipitate of ammonium phosphomolybdate. Also the precipitate obtained is soluble in solution of Ammonia.
Hence we can say assertion is true and reason is also true.

So, Option A is correct.

Additional information:
Other qualitative test to identify the presence of the Phosphate ions are:
Phosphate ion reacts with Silver nitrate to form a yellow precipitate of silver phosphate ($A{g_3}P{O_4}$)
Phosphate ion reacts with Barium Chloride to form a white precipitate of Barium Phosphate ($B{a_3}{(P{O_4})_2}$)

Note: Phosphate ion is a weak oxidising agent and it dissolves in water to form a basic solution. The reason for its being a weak oxidizing agent is that phosphorus in Phosphate ion ($PO_4^{3 - }$).