KVPY SX SB Exam 2015 Question Paper

Loudness of sound in decibel Loudness of sound in decibel $\mathit{d}\mathit{B}=10{\log }_{10}\left(\frac{\mathit{I}}{{\mathit{I}}_0}\right)$
when intensity of sound become 100 I then new decibel level = $\mathit{d}\mathit{B}\prime =10{\log }_{10}\left(\frac{100\mathit{I}}{{\mathit{I}}_0}\right)$
dB' – dB = 10 log${}_{10}$100
dB' – dB = 20
∴ decibel rise by 20 dB
only one option i.e. 80 to 100 dB match with it