Ms Sweta,
Notice period is for serving the company during the period, however it is the discretion of the company, to allow adjustment of leave, normally it is not allowed. Notice period is meant for looking for a suitable substitute in the place of employee leaving the company. It is also the duty of the leaving employee to handover the complete charge of his duties to his successor and get him acclimatised to the working of the company. If the leaving employee chooses to pay for the notice period he cannot be stopped.
Regards.
Joga Rao