Based upon location in the periodic table, the formula for beryllium (be) chloride (cl) is:
a be2cl
b be2cl3
c becl2
d be3cl4

Explanation: For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.  

Here beryllium is a metal and can lose 2 electrons to form a cation and chlorine can accept one electron to form an anion.

The cations and anions being oppositely charged attract each other through strong coloumbic forces and form an ionic bond.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.