Q.Photons of wavelength $\lambda$ are incident on a metal. The most energetic electrons ejected from the metal are bent into a circular arc of radius $R$ by a perpendicular magnetic field having magnitude $B$. The work function of the metal is (KVPY-SX 2016) [options illegible in the source scan -- the four answer choices are rendered with corrupted, overlapping symbol-font glyphs across the page break and cannot be reliably reconstructed]