How many molecular orbitals are present in the valence band of a sodium crystal with a mass of 7.90 g?

Number of atoms equal the number of molecular orbitals as each atom has 1 atomic orbital and 1 electron.

Therefore,

Number of atoms = (mass/molar mass) * Avogadro's number = (7.90/22.99) * 1.36*10^23 = 4.67*10^22 atoms.

Then,

Number of molecular orbitals = 4.67*10^22