A signal is said to be periodic if TTs is a rational number.
In the case, T = √2Ts
√2 is not a rational number. So it is not periodic.
In the case, T = 1.2 Ts
⇒TTs=65 which is a rational number and this is periodic.
A sampled signal is not always periodic for all type of signals. So option (c) and (d) are not valid here.
Hence, Only option (b) is correct.