Two metals A and B have work functions 4eV and 10eV respectively. Which metal has the higher threshold wavelength ?

Explanation

Work function `W =hv_(0) =( hc)/( lambda_(0))`
`lambda_(0) prop ( 1)/( W )`
As `W_(A) lt W_(B), ( lambda_(0))_(A) gt ( lambda_(0) )_(B)`
i.e., threshold wavelength of metal A is higher.