19) C

Frequency = (5 ÷ 10⁻¹³) = 5 x 10¹³ (PLEASE LEARN THE POWERS RULES)

Energy = f x h = 5 x 10¹³ x 6.63 x 10⁻³⁴

= 33.15 x 10⁻²¹

= 3.32 x 10⁻²⁰ J