The radius of which of the following orbit is same as that of the first Bohr's orbit of hydrogen atom?

According to molecular orbital theory which of the following statement about the magnetic character and bond order is correct regarding $$O_2^+$$

A sodium salt on treatment with MgCl₃ gives white precipitate only on heating. The anion of the sodium salt is

If $$\omega $$ $$\left( { \ne 1} \right)$$ be a cube root of unity and $${\left( {1 + {\omega ^2}} \right)^n} = {\left( {1 + {\omega ^4}} \right)^n},$$ then the least positive value of n is