Hi,
Hope you are doing well !!
Yes, he will be able to take the benefit of exemption u/s 54.
Under Section 54 of the Income Tax Act, a taxpayer having long-term capital gains from sale of a residential property can avoid the same by purchasing or constructing a residential property 1 year before or 2 year after (in case of purchase of property) or before 3 years (in case of construction of property).
The amount of exemption under Section 54 of the Income Tax Act for the long-term capital gains will be the lower of:
Capital gains arising on transfer of residential house.
or
Investment made in purchase or construction of a new residential house property. Hence, the balance capital gains (If any) will be taxable.