Electromagnetic Spectrum & Atmosphere question from NEET 1999 (AIPMT)

Answer: (a)

1. Ozone strongly absorbs UV with wavelength below about $300\ \text{nm}$.
2. $300\ \text{nm} = 3\times10^{-7}\ \text{m}$.
3. So the answer is (a) less than $3\times10^{-7}\ \text{m}$.