Which of the following has the lowest melting point?

$A$ small fish $0.4\, m$ below the surface of a lake is viewed through a simple converging lens of focal length $3\, m$. The lens is kept at $0.2\, m$ above the water surface such that the fish lies on the optical axis of the lens. The image of the fish seen by the observer will be at (given $\mu_{water} = 4/3$):

The $pK_a$ of a weak acid is $4.8$. What should be the ratio of $[Acid]/[Salt]$ of a buffer if $pH = 5.8$ is required?

If $\frac{{{{({2^{n + 1}})}^m}({2^{2n}}){2^n}}}{{{{({2^{m + 1}})}^n}{2^{2m}}}} = 1$,then $m =$

$A$ ball of mass $160\, g$ is thrown up at an angle of $60^\circ$ to the horizontal at a speed of $10\, m\,s^{-1}$. The angular momentum of the ball at the highest point of the trajectory with respect to the point from which the ball is thrown is nearly ........ $kg\, m^2/s$ $(g = 10\, m\,s^{-2})$.

The surface of a metal is illuminated with light of wavelength $400 \, nm$. The kinetic energy of the ejected photoelectrons is found to be $1.68 \, eV$. The work function of the metal is .................. $eV$ $(hc = 1240 \, eV-nm)$.