The $pK_a$ of a weak acid $HA$ is $4.5$. The $pOH$ of an aqueous buffered solution of $HA$ in which $50\%$ of the $HA$ acid is ionized is

The maximum value of $\frac{\log x}{x}, 0 < x < \infty$ is

Which of the following is the correct order of acidic strength?

Among the following compounds,which one is not responsible for the depletion of the ozone layer?

$A$ hollow pipe of length $0.8 \ m$ is closed at one end. At its open end,a $0.5 \ m$ long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is $50 \ N$ and the speed of sound is $320 \ ms^{-1}$,the mass of the string is: (in $g$)

$Ni$ anode is used in the electrolytic extraction of