Given: Wavelength λ = 686 nm convert to meter λ = 6.86 x 10⁻⁷ m
Velocity of light c = 3.00 x 10⁸ m/s
Required: Frequency f = ?
Formula: f = c/λ
f = (3.00 x 10⁸ m/s)/(6.86 x 10⁻⁷ m)
f = 4.37 x 10¹⁴ Hz or
f = 437 Terahertz
I think its b too but i may be wrong
weight = mass*g is the formula