In a hydrogen atom, the electron is in excited state. It comes down to the first excited state by emitting 10 different wavelengths. The value of n is
Number of possible emission lines are n(n - 1)/2 when an electron jumps from state to ground state. In this question, this value should be (n - 1) (n - 2)/2.
Hence,
Solving this, we get n = 6.