Ratio of longest wave lengths corresponding to Lyman and Balmer series in hydrogen spectrum is

The transition from the state n = 3 to n = 1 in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from

The half life of a radioactive nucleus is 50 days. The time invertal (t₂ $$-$$ t₁) between the time t₂ when $${2 \over 3}$$ of it has decayed and the time t₁ when $${1 \over 3}$$ of it had decayed is

A mixture consists of two radioactive materials A₁ and A₂ with half lives of 20 s and 10 s respectively. Initially the mixture has 40 g of A₁ and 160 g of A₂. The amount of the two in the mixture will become equal after