Answer
(a) Na$_{2}$Se
(b) NiBr$_{2}$
(c) N$_{2}$O$_{5}$
(d) CuSO$_{4}$
(e) (NH$_{4}$)$_{2}$SO$_{3}$
Work Step by Step
(a) Na$_{2}$Se
Sodium (Na) is an alkali metal (group 1A) and has a valence of 1+. Selenium (Se) is in group 6A and has a valence of 2-. We see that sodium and selenium are present in this compound in a 2:1 ratio.
(b) NiBr$_{2}$
Nickel (Ni) is a transition metal and has more than one valence. We want the nickel atom that has a valence of 2+ as specified by the Roman numeral II following its name. Bromine (Br) is a halogen (group 7A) and has a valence of 1-. We see that nickel and bromine are present in this compound in a 1:2 ratio.
(c) N$_{2}$O$_{5}$
According to the name of this molecular compound, there are two atoms of nitrogen (N) for every five atoms of oxygen (O).
(d) CuSO$_{4}$
Copper (Cu) is a transition metal and has more than one valence. We want the copper atom that has a valence of 2+ as specified by the Roman numeral II following its name. Sulfate is an oxoanion with a valence of 2-. We see that copper and sulfate ions are present in this compound in a 1:1 ratio.
(e) (NH$_{4}$)$_{2}$SO$_{3}$
Ammonium (NH$_{4}$) is a polyatomic cation with a valence of 1+. Sulfite (SO$_{3}$) is an oxoanion with a valence of 2-. We see that ammonium and sulfite are present in this compound in a 2:1 ratio.
