Answer: D. The number of molecules having Er or greater doubles.
Explanation: As the temperature increases from 20°C to 30°C, the number of molecules with maximum energy decreases, but the number of effective collisions which result into the formation of product doubles.
This is due to doubling of molecules which possess energy equal to or greater than \(E_r\) which means now double number of molecules will be able to cross the energy barrier and hence the formation of product increases and hence the rate increases to double.
