To determine the electronegativity for each bond you need to calculate the difference of electronegativity of the atoms forming the bond.
If the difference is equal or greater than 1.7 you have an ionic bond.
If the difference is between 0.4 and 1.6 you have a polar covalent bond.
If the difference is between 0 and less than 0.4 you have a nonpolar covalent bond.
1) In NH₃ there is a nitrogen - hydrogen bond.
electronegativity of nitrogen - electronegativity of hydrogen =
3 - 2.2 = 0.8 → polar covalent bond
2) In N₂ there is a nitrogen-nitrogen bond.
electronegativity of nitrogen - electronegativity of nitrogen =
3 - 3 = 0 → nonpolar covalent bond
3) In H₂O there is an oxygen - hydrogen bond.
electronegativity of oxygen - electronegativity of hydrogen =
3.5 - 2.2 = 1.3 → polar covalent bond
4) In PCl₃ there is a chlorine - phosphorus bond.
electronegativity of chlorine - electronegativity of phosphorus = 3 - 2.1 = 0.9 → polar covalent bond
4) In HBr there is a bromine - hydrogen bond.
electronegativity of bromine - electronegativity of hydrogen = 2.8 - 2.2 = 0.6 → polar covalent bond
5) In MgCl₂ there is a chlorine - magnesium bond.
electronegativity of chlorine - electronegativity of magnesium = 3 - 1.2 = 1.8 → ionic bond
6) In F₂ there is a fluorine - fluorine bond.
electronegativity of fluorine - electronegativity of fluorine =
4 - 4 = 0 → nonpolar covalent bond
7) In CO₂ there is an oxygen - carbon bond.
electronegativity of oxygen- electronegativity of carbon =
3.5 - 2.5 = 1 → polar covalent bond
8) In LiCl there is a chlorine - lithium bond.
electronegativity of chlorine - electronegativity of lithium =
3 - 1 = 2 → ionic bond
9) In Na₂O there is an oxygen - sodium bond.
electronegativity of oxygen - electronegativity of sodium =
3.5 - 0.9 = 2.6 → ionic bond
10) In CCl₄ there is a chlorine - carbon bond.
electronegativity of chlorine - electronegativity of carbon =
3 - 2.5 = 0.5 → polar covalent bond
and Nitride's is 