Question

What is the formula of ammonium nitrate?
A) $AlC{l_3}$
B) $N{H_4}Cl$
C) $Al{\left( {N{O_3}} \right)_3}$
D) $N{H_4}N{O_3}$

Answer 1

We have to remember that ammonium has a positive charge whereas nitrate has a negative charge, since both have the same valence thus it is easy to get the chemical formula. Valence tells how many free ions a compound or element has which is therefore useful in getting the chemical formula.

Complete step by step by answer:
Before solving this question you need to know about the charges of the following compound given let’s start.
Ammonium cation has a chemical formula $N{H_4}^ +$ and it a positively charged species , It is generally formed by the protonation of Ammonia ($N{H_3}$)
$N{H_3} + \;{H^ + } \to NH_4^ +$
Nitrate is a negatively charged species having a chemical formula $N{O_3}^ -$. It is generally formed when a nitric acid loses its proton
$HN{O_3} \to {H^ + } + NO_3^ -$
So thus it is easy to form a formula for this compound since we get the valence electron or charges on it.

Option A) This option is incorrect since $Al$represents aluminium and the question clearly asks Ammonium so we can neglect this option.
$AlC{l_3}$, the correct answer for this is Aluminium chloride.
Option B) This option is incorrect although it has Ammonium ($N{H_4}$) in it so you might get confused or tick this option in hurry seeing ammonium first but it has chloride ($Cl$) in it.
$N{H_4}Cl$, the correct answer for this is Ammonium chloride.
Option C) This is an incorrect option since$Al$represents Aluminium and the question clearly asks Ammonium so we can neglect this option.
$Al{\left( {N{O_3}} \right)_3}$, the correct answer for this is Aluminium nitrate.
Option D) it is correct as it has both the cation and anion same asked in the question.
$N{H_4}N{O_3}$, formula for this compound is Ammonium nitrate.

Hence, the correct option is D.

Note: It is easy to get the chemical formula for the compound if you know the valency or charge of an element. Once you know the value of the charges and if you can identify the chemical formula for a particular element then it’s easy to solve these types of questions.