It allows you to determine the relation between the reactants and the products.
The answer is d, hand soap.
Hand soap is alkaline and red litmus paper turns blue when exposed to alkaline solution.
The equation is
W = C/F
W= 3.00 x 10^8 m/sec
——————————
6.165 x 10^14 Hz
W= 4.87 x 10^-7 m
Energy is
E=hF
E= (6.626 x 10^-34 Jxsec )(6.165 x 10^14 Hz)
E= 4.085 x 10^-19 J