Two categories of compounds are
(1) covalent and molecular
(2) covalent and metallic
(3) ionic and molecular
(4) ionic and metallic

Answer is: (3) ionic and molecular.

Ionic compounds are made of ions held together with ionic bonds.

Ionic bond forms when a cation transfers its extra electron to an anion who needs it.  

For example compound magnesium chloride (MgCl₂) has ionic bond (the electrostatic attraction between oppositely charged ions).  

Magnesium (metal) transfers two electrons (became positive cation) to chlorine (became negative anion).  

Molecular compounds are made up of molecules whose atoms are connected with covalent bonds.

Covalent bond is bond between nonmetals.  

For example, molecule carbon monoxide CO has covalent bond.

Carbon (C) and oxygen (O) are nonmetals.  

Carbon atom and oxygen atom are connected by a triple bond (six shared electrons in three bonding molecular orbitals) that is formed of two covalent bonds and one dative covalent bond.  

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.