Which of these is a covalent compound?

a. mgo

b. licl

c. alcl3

d. co

CO  

The nature of the bond is related to the distance between them and it also depends on how positive or negative they are. When two atoms approach each other the electrons of each other are attracted to the protons of other. So when atom is attracted to another it gets stressed out by the attractive forces and tries to relive the stress by getting closer. The pull is so strong that the energy level rises when they are separate  

A bond formed by atoms sharing electrons is called covalent bond. The strength with which an atom holds shared electron is called electronegativity. CO is a covalent compound because they share a lone pair of electrons and two ordinary covalent bonds between the carbon and the oxygen atom

n+h→nh3

we must remember that nitrogen and hydrogen are both diatomic molecules in their standard gas form. this adjusts the equation to

n2+h2→nh3

now we need to adjust coefficients in order to balance the atoms on each side of the equation. currently we have 2 atoms of nitrogen and 2 atoms of hydrogen on the reactant side and 1 atom of nitrogen and 3 atoms of hydrogen on the product side.

we can balance the hydrogens by placing a coefficient of 2 in front of ammonia and a coefficient of 3 in front of the hydrogen.

n2+3h2→2nh3

this gives us 6 hydrogen on each side and coincidentally the nitrogens now equal 2 on each side.

i think   the answer is c hope i'm right