1.

NI$_3$ is called as nitrogen triiodide. Here the prefix $color{#c34632}text{tri-}$ indicates that the ratio of nitrogen to iodine in the compound is $1:3$.

2.

CCl$_4$ is called as tetrachloro methane. Here the prefix $color{#c34632}text{tetra-}$ indicates that the ratio of carbon to chlorine in the compound is $1:4$.

3.

OF$_2$ is called as oxygen difluoride. Here the prefix $color{#c34632}text{di-}$ indicates that the ratio of oxygen to fluorine in the compound is $1:2$.

4.

P$_2$O$_5$ is called as diphosphorus pentaoxide. Here the prefix $color{#c34632}text{di-}$ and $color{#c34632}text{penta-}$ indicates that the ratio of phosphorus to oxygen in the compound is $2:5$.

4.

N$_2$O$_3$ is called as dinitrogen trioxide. Here the prefix $color{#c34632}text{di-}$ and $color{#c34632}text{tri-}$ indicates that the ratio of nitrogen to oxygen in the compound is $2:3$.

a.

Carbon monoxide is CO. Here the prefix $color{#c34632}text{mono-}$ indicates that the ratio of both elements in the compound is $1:1$.

b.

Sulfur tetrafluoride is SF$_4$. Here the prefix $color{#c34632}text{tetra-}$ indicates that each sulfur atom is bonded with 4 fluorine atoms.

c.

Dinitrogen tetraoxide is N$_2$O$_4$ Here the prefix $color{#c34632}text{di-}$ and $color{#c34632}text{tri-}$ indicates that the ratio of nitrogen to oxygen in the compound is $2:4$.

d.

Nitrogen tribromide is NBr$_3$. Here the prefix $color{#c34632}text{tri-}$ indicates that each nitrogen atom is bonded with 3 bromine atoms.

e.

Carbon disulfide is CS$_2$. Here the prefix $color{#c34632}text{di-}$ indicates that each carbon atom is bonded with 2 sulfur atoms.

a.

SO$_2$ is sulfur dioxide. It is made up of sulfur and oxygen. Both elements are non-metals therefore this compound is molecular in nature.

b.

PbO$_2$ is lead dioxide. It is made up of lead and oxygen. Lead is a metal therefore this compound is ionic in nature.

c.

AlCl$_3$ is aluminum chloride. It is made up of aluminum and chlorine. Aluminum is a metal therefore this compound is ionic in nature.

d.

N$_2$O is dinitrogen monoxide. It is made up of nitrogen and oxygen. Both elements are non-metals therefore this compound is molecular in nature.

e.

KClO$_3$ is potassium chlorate. It is made up of potassium, chlorine and oxygen. Potassium is a metal therefore this compound is ionic in nature.

f.

SnO$_2$ is tin oxide. It is made up of tin and oxygen. Tin is a metal therefore this compound is ionic in nature.

g.

FePO$_4$ is iron phosphate. It is made up of iron, phosphorus and oxygen. Iron is a metal therefore this compound is ionic in nature.

h.

N$_2$O$_4$ is dinitrogen tetraoxide. It is made up of nitrogen and oxygen. Both elements are non-metals therefore this compound is molecular in nature.

b.

Hydrogen requires $2-1=1$ electron to obtain a stable configuration.

Oxygen requires $8-7=1$ electron to obtain a stable configuration.

c. Molecular compound of H$_2$O.

In the diagram of hydrogen chloride, it can be seen that $1$ electron of hydrogen is begin shared with 1 electron of chlorine. Both atoms have obtained a stable configuration by sharing of electron to form a stable molecule. In the diagram of sodium chloride, it can be seen that sodium has lost its electron to chlorine for both atoms to obtain a stable configuration. This transfer of electron results in an ionic compound and not a molecule.

The atomic number of chlorine is 17. This implies that it has 17 protons and 17 electrons. This further implies that there are 7 electrons in the outermost orbit of each chlorine atom. Each chlorine atom requires just 1 more electron to obtain a stable electronic configuration. This can be obtained by 2 chlorine atoms each sharing one of their valence electron to form the molecule Cl$_2$. This is the reason that chlorine exists as a diatomic molecule and not monoatomic particles.

The formula H$_2$O$_2$ implies that the molecule consists of 2 hydrogen atoms and 2 oxygen atoms, where by HO will mean that each molecule consists of 1 hydrogen and 1 oxygen atom which is technically incorrect.