the second try is correct. for FCC, contribution per unit cell is 4. the at atom at corner contributes 1/8. if we ignore that, we get 3. (B is not at corners). thus, we get AB3 only.
check it out in your NCERT. it's explained in a great way.
Acc. To kelper's law, the sun is at one of the focus of the planet's path. It's an ellipse having two focus and two directrix. Do all the paths of planet, have different foci and directrix or have common focus and directrix?
When we add NaCl to water, it dissociates into sodium and chloride ions. Why the sodium cation not joined with the lone pair of electrons on oxygen, whereas in case of HCl, hydrogen joins with those lone pairs of electrons?