Question

__ cu(no₃)₂ + na₃po₄ → cu₃(po₄)₂ + __ nano₃

Explanation:

Step1: Balance copper atoms

There are 3 copper atoms in $Cu_3(PO_4)_2$, so we need 3 moles of $Cu(NO_3)_2$.
$3Cu(NO_3)_2+ \underline{\hspace{2cm}}Na_3PO_4
ightarrow1Cu_3(PO_4)_2+\underline{\hspace{2cm}}NaNO_3$

Step2: Balance phosphate groups

There are 2 phosphate groups in $Cu_3(PO_4)_2$, so we need 2 moles of $Na_3PO_4$.
$3Cu(NO_3)_2 + 2Na_3PO_4
ightarrow1Cu_3(PO_4)_2+\underline{\hspace{2cm}}NaNO_3$

Step3: Balance sodium and nitrate groups

From 2 moles of $Na_3PO_4$, we have 6 sodium atoms. And from 3 moles of $Cu(NO_3)_2$, we have 6 nitrate groups. So we need 6 moles of $NaNO_3$.
$3Cu(NO_3)_2+2Na_3PO_4
ightarrow1Cu_3(PO_4)_2 + 6NaNO_3$

Answer:

3, 2, 1, 6