The correct options are
A maximum pressure variation is BAK
B maximum density variation is
ρAK C pressure equation and density equation are in phase
There are three equations associated with any longitudinal wave .
y(x,t),ΔP(x,t),and Δρ(x,t)
y represents displacement of medium particles from their mean position parallel to direction of wave velocity .
From y(x,t) equation we can make ΔP(x,t) and Δρ (x,t) equation by using fundamental relations between them ,
ΔP=−Bdydx and Δρ = - ρ dydx
Pressure amplitude = BAK and density amplitude = ρAK
Therefore A and B are correct options.
ΔP(x,t) and Δρ(x,t) are in same phase . But y(x,t)has a phase difference of π/2 with rest two equations .
Therefore C is correct and D is wrong option