8. 2(nh₄)₃po₄ n= h= p= o=

Explanation:

Step1: Analyze nitrogen atoms

In one $(NH_4)_3PO_4$ unit, there are 3 nitrogen atoms from the 3 ammonium ($NH_4$) groups. Since there are 2 formula - units of $(NH_4)_3PO_4$, the number of nitrogen atoms $N = 2\times3=6$.

Step2: Analyze hydrogen atoms

In one $(NH_4)_3PO_4$ unit, there are $4\times3 = 12$ hydrogen atoms from the 3 ammonium ($NH_4$) groups. For 2 formula - units, the number of hydrogen atoms $H=2\times12 = 24$.

Step3: Analyze phosphorus atoms

In one $(NH_4)_3PO_4$ unit, there is 1 phosphorus atom. For 2 formula - units, the number of phosphorus atoms $P = 2\times1=2$.

Step4: Analyze oxygen atoms

In one $(NH_4)_3PO_4$ unit, there are 4 oxygen atoms. For 2 formula - units, the number of oxygen atoms $O=2\times4 = 8$.

Answer:

$N = 6$, $H = 24$, $P = 2$, $O = 8$