The wavelength of the second line of Balmer series is 486.4 nm. What is the wavelength of the first line of Lyman series?

The Lyman series of a hydrogen atom belongs in which category

If an electron in hydrogen atom jumps from an orbit of level $$n=3$$ to an orbit at level $$n=2$$, emitted radiation has a frequency of

(R = Rydberg's constant and c = velocity of light)

Ba-122 has half-life of 2 min. Experiment has to be done using Ba-122 and it takes 10 min to set up the experiment. It initially 80 g at Ba-122 was taken, how much Ba was left when experiment was started?