then ${y_{reflected}} = a\sin (\omega t + kx + \pi ) = - a\sin (\omega t + kx)$
Superimposition of these two waves give the required stationary wave.

|
$(A)$ Temperature of gas is made $4$ times and pressure $2$ times |
$(P)$ Speed becomes $2\sqrt 2$ times |
|
$(B)$ Only pressure is made $4$ times without change in temperature |
$(Q)$ Speed become $2$ times |
|
$(C)$ Only temperature is changed to $4$ times |
$(R)$ Speed remains unchanged |
|
$(D)$ Molecular mass of the gas is made $4$ times |
$(S)$ Speed becomes half |