As we know, when electron jumps from higher energy state to first energy state (n=2), the spectrum of light is called Balmer series. So obviously option (a) is wrong because this option comes under Lyman series and option (b) is correct. Now as we defined Balmer series condition so option (c) is also wrong. Also we know that spectrum lines become closer if electron jumps from higher energy state to ground state so option (d) is also correct.

Therefore option (b) & (d) are correct.