When an excess of $NaOH$ solution is added to a solution of potassium alum,what do we obtain?

The equivalent weight of phosphoric acid $(H_3PO_4)$ in the reaction,$NaOH + H_3PO_4 \to NaH_2PO_4 + H_2O$ is

$Br_2 + 2X^{-} \to 2Br^{-} + X_2$
$Cl_2 + 2Y^{-} \to 2Cl^{-} + Y_2$
The incorrect match regarding the above reactions is:

Liquids $A$ and $B$ form an ideal solution. If $X_A$ and $Y_A$ are the mole fractions of $A$ in the solution and in vapour phase in equilibrium,respectively,then (Given $P_A^o > P_B^o$):

The speed of sound in oxygen $(O_2)$ at a certain temperature is $460 \; m/s$. The speed of sound in helium $(He)$ at the same temperature will be (assume both gases to be ideal): (in $; m/s$)

$A$ sound absorber attenuates the sound level by $20\, dB$. The intensity decreases by a factor of: