The temperature coefficient of a reaction is 2 . When the temperature is increased from $30°\mathrm{C}$ to $90°\mathrm{C}$, the rate of reaction is increased by
 

Temperature coefficient gives the ratio of the rate of a reaction when the temperature increases by $10 \mathrm{K}$
When the temperature increases from $30°\mathrm{C}$ to $90°\mathrm{C}$ the reaction rate is increased $2^6$times. i.e. 64 times since there is 6 times $10 \mathrm{K}$ rise in temperature.