P:
$Y * Z = Y * (X*Y)$
$= Y * (XY + X'Y')$
$= Y (XY + X'Y') + Y' (XY + X'Y')'$
$= XY + Y' ((X' + Y') (X+ Y))$
$= XY + Y' (X'Y + XY')$
$= XY + XY'$
$= X(Y + Y')$
$= X$
So, P is valid.
Q:
$X * Z = X * (X*Y)$
$= X * (XY + X'Y')$
$= X (XY + X'Y') + X' (XY + X'Y')'$
$= XY + X' ((X' + Y') (X+ Y))$
$= XY + X' (X'Y + XY')$
$= XY + X'Y$
$= Y(X + X')$
$= Y$
So, Q is also valid.
R:
$X * Y * Z = (X * Y) * (X * Y)$
$= (XY + X'Y') * (XY + X'Y')$
$= (XY + X'Y') (XY + X'Y') + (XY + X'Y')' (XY + X'Y')'$
$= (XY + X'Y') + (XY + X'Y')' (\because AA = A)$
$= 1 (\because A + A' = 1)$
So, R is also valid.
Hence, D choice.