The number of photons emitted by a monochromatic (single frequency)...

Energy emitted in $0 . 1sec$

$= 0 . 1sec \times {10}^{- 3}J{s}^{- 1}$

$= {10}^{- 4}J$

If 'n' photons of $\lambda = 1000nm$ are emitted, then ${10}^{- 4} = \dfrac{nhc}{\lambda}$

${10}^{- 4} = \dfrac{n \times 6 . 63 \times {10}^{- 34} \times 3 \times {10}^{8}}{1000 \times {10}^{- 9}}$

$n = 5 . 02 \times {10}^{14} = 50 . 2 \times {10}^{13}$

$n = 50$ (nearest integer)