In the atomic spectrum of hydrogen, the wavelengths of the spectral lines corresponding to electronic transitions (i) $n=4$ to $n=2$ and (ii) $n=3$ to $n=1$ are $\lambda_1$ and $\lambda_2 \mathop {\rm{A}}\limits^{\rm{o}}$ respectively. The value of ( $\lambda_1-\lambda_2$ ) (in cm ) is ( $R_{\mathrm{H}}=$ Rydberg constant)

Work functions of four metals $M_1, M_2, M_3$ and $M_4$ are $4.8,4.3,4.75$ and 3.75 eV respectively. The metals which do not show photoelectric effect when light of wavelength 310 nm falls on the metals are

In second period of the modern periodic table, two elements $X$ and $Y$ have higher first ionisation enthalpy values than the preceding and succeeding elements. $X$ and $Y$ are respectively

Consider the following pairs of elements and identify the pairs of elements which have nearly same atomic radius.

I. Y, La

II. Zr, Hf

III. Mo, W

IV. Cr, Mo