Dear Sir,
In order to provide correct view, further information would be required.
1. The name and nature (Government/Non-government) of Employer of such person.
2. Whether the person has received any gratuity from his employer after retirement.
3. Whether the person received periodic pension also and the total amount of pension receivable.
If the person worked for the Government and has received full pension in one lump sum amount, then whole of the lump sum pension received would be exempt from tax.
If the person worked for Non government employer and has received full pension in one lump sum amount, and has also received gratuity, then 1/3rd of the lump sum pension received would be exempt from tax.
If the person worked for Non government employer and has received full pension in one lump sum amount, and has not received any gratuity, then half of the lump sum pension received would be exempt from tax.
The law relating to taxability of Commuted (Lump sum) Pension can be referred to in Section 10 (10A) of the Income Tax Act, 1961.
Hope this helps.