How many unshared pairs of electrons does the nitrogen atom in ammonia possess?

In order to find the number of unshared electrons present on N atom in Ammonia (NH₃), we will first draw the lewis structure of Ammonia.

Step 1: Calculate number of Total valence Electrons:

# of Valence e⁻s in N   =  5

# of Valence e⁻s in H₁  =  1

# of Valence e⁻s in H₂  =  1

# of Valence e⁻s in H₃  =  1
                                   
Total Valence e⁻s         =  8

Step 2: Start drawing the structure:

Draw Central atom (N) in center surrounded by three H atoms. Connect N with each H atom through single bond and subtract e elctrons from total valence electrons for each single bon. Therefore, for three single bonds, 6 electrons are subtracted. i.e.

                              =  8  -  6

                              =  2

These two electrons left are added to N atom as a lone pair of electron.

Result:
           Nitrogen atom in Ammonia possess 2 (two) unshared electrons marked as red in given picture.

because it's composed of two elements, hydrogen and oxygen. water is technically a molecular compound tho, for it has two hydrogens.