Which formula represents a polar molecule?
(1) o2
(2) co2
(3) nh3
(4) ch4

Option (3) is the correct answer.

Explanation:

A molecule is polar when the net dipole moment of molecule is zero. When an electronegative atom is attached to an electropositive atom then the electronegative atom pulls the shared pair of electrons more towards itself.

As a result, the movement of electrons is more towards the electronegative atom and the dipole moment becomes zero. This will also induce partial positive and partial negative charge on electropositive and electronegative atom.

On the other hand, are covalent compounds and does not have a net zero dipole moment.

Thus, we can conclude that out of the given options  represents a polar molecule.

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.