Question

select the correct answer.
what is the chemical formula for the compound ammonium phosphate? use the list of polyatomic ions and the periodic table to help you answer.
a. $\ce{nh4h2po4}$
b. $\ce{(nh4)2po4}$
c. $\ce{(nh4)3po4}$
d. $\ce{(nh4)4po4}$

chemical name	chemical formula	chemical name	chemical formula
carbonate	$\ce{co3^{2-}}$	ammonium	$\ce{nh4^+}$
hypocarbonite	$\ce{co2^-}$	cyanide	$\ce{cn^-}$
hydrogen carbonate (bicarbonate)	$\ce{hco3^-}$	hydroxide	$\ce{oh^-}$
chlorite	$\ce{clo2^-}$	peroxide	$\ce{o2^{2-}}$
hypochlorite	$\ce{clo^-}$	phosphate	$\ce{po4^{3-}}$
chlorate	$\ce{clo3^-}$	hydrogen phosphate	$\ce{hpo4^{2-}}$

Explanation:

Step1: Identify ions

Ammonium ion: $NH_4^+$ (charge +1). Phosphate ion: $PO_4^{3-}$ (charge -3).

Step2: Balance charges

To balance, find ratio: Let $x$ = number of $NH_4^+$, $y$ = number of $PO_4^{3-}$.
Charge balance: $x(+1) + y(-3) = 0$ → $x = 3y$.
Take $y = 1$, then $x = 3$. So formula: $(NH_4)_3PO_4$.

Answer:

C. $(NH_4)_3PO_4$