Be²⁺ is isoelectronic with which of the following ions ?

What is the maximum number of orbitals that can be identified with the following quantum numbers ?
n = 3, l = 1, m₁ = 0

According to law of photochemical equivalence the energy absorbed (in ergs/mole) is given as (h = 6.62 $$ \times $$ 10^$$-$$27 ergs, c = 3 $$ \times $$ 10¹⁰ cm s^$$-$$1, N_A = 6.02 $$ \times $$ 10^$$-$$23 mol^$$-$$1)

The outer electronic configuration of Gd (At. No. 64) is