The correct option is A (a)→(ii),(b)→(iii),(c)→(iv),(d)→(i)
On moving left to right in periodic table, ionisation energy increases (generally) but group-13 elements have lesser I.E. than group-2 elements due to stable ns2 electronic configuration of group-2 elements and group-15 elements have greater I.E. than group-16 elements due to half-filled stable np3 electronic configuration of group-15 elements.
∴ Overall order of I.E should be
c>b>a>d
Hence, D is the correct option.