Select the correct pair from the following.

$A$ speaker emits a sound wave of frequency $f_0$. When it moves towards a stationary observer with speed $u$,the observer measures a frequency $f_1$. If the speaker is stationary,and the observer moves towards it with speed $u$,the measured frequency is $f_2$. Then:

Statement$-1$ : Toluene is more reactive than benzene in chlorination.
Statement$-2$ : During the nitration of Toluene $\stackrel{\oplus}{ N } O _2$ acts as electrophile.

$A$ sound absorber attenuates the sound level by $20\, dB$. The intensity decreases by a factor of

The $IUPAC$ name of $(CH_3)_2CH-CH_2-CH_2Br$ is

Sugar found in $RNA$.