Light of which of the following wavelengths can we see?

Think it through first, then pick an option.

a 400 m
b 700 cm
c 652 nm
d 600 am

Answer and explanation

Correct answer: c 652 nm

Only wavelengths from 400 nm to 700 nm are seen as light, and 652 nm is inside that range. 400 m and 700 cm are far too long (radio range) and 600 am (10⁻¹⁸ m) is far too short.

Why the other options are wrong

a 400 m: This is not the answer: Only wavelengths from 400 nm to 700 nm are seen as light, and 652 nm is inside that range. 400 m and 700 cm are far too long (radio range) and 600 am (10⁻¹⁸ m) is far too short.
b 700 cm: This is not the answer: Only wavelengths from 400 nm to 700 nm are seen as light, and 652 nm is inside that range. 400 m and 700 cm are far too long (radio range) and 600 am (10⁻¹⁸ m) is far too short.
d 600 am: This is not the answer: Only wavelengths from 400 nm to 700 nm are seen as light, and 652 nm is inside that range. 400 m and 700 cm are far too long (radio range) and 600 am (10⁻¹⁸ m) is far too short.