The work functions of Cesium and Platinum are 1.9 eV and 5.7 eV, respectively. The ratio of their threshold wavelengths, respectively is

3 : 1

The correct answer is Option (2) → 3 : 1

Given:
Work functions — Cesium: $W_1 = 1.9\,eV$, Platinum: $W_2 = 5.7\,eV$

Threshold wavelength is given by:
$\lambda = \frac{hc}{W}$

Therefore, ratio of threshold wavelengths:

$\frac{\lambda_1}{\lambda_2} = \frac{W_2}{W_1}$

Substituting values:

$\frac{\lambda_1}{\lambda_2} = \frac{5.7}{1.9} = 3$

Ratio of threshold wavelengths (Cesium : Platinum) = 3 : 1