Energy of nth orbit ∝ 1/ n2 Thus E1=C/(1) second orbit E2=C/(2)2=C/(4)third orbit energy E3=C/(3)2=C/(9) Difference E1 - E2=C (3/4) Difference E2 - E3=C (5/36) Thus ratio=3/4 ÷ 5/36=27/5Answer: (d)