A water supply scheme transports $10\:MLD$ (MIllion Litres per Day) water through a $450\:mm$ diameter pipeline for a distance of $2.5\:km$. A chlorine dose of $3.50\:mg/litre$ is applied at the starting point of the pipeline to attain a certain level of disinfection at the downstream end. It is decided to increase the flow rate from $10\:MLD$ to $13 MLD$ in the pipeline. Assume exponent for concentration, $n=0.86$. With this increased flow, in order to attain the same level of disinfection, the chlorine dose (in $mg/litre$) to be applied at the starting point should be
1. $3.95$
2. $4.40$
3. $4.75$
4. $5.55$