Electronegativity and Electron Gain Enthalpy

Q. Which of the following does not lose an electron easily
1)Na
2)F
3)Mg
4)Al

Q. Which of the following sets has strongest tendency to form anions?

1. Ga, Ni, Tl
2. N, O, F
3. Na, Mg, Al
4. V, Cr, Mn.

Q. $F-$centres are :

1. the electrons trapped in anionic vacancies
2. the electron trapped in cationic vacancies
3. non-equivalent sites of stoichiometric compound
4. All of the above