If I have 977 units of a mutual fund and after 5 years it merges with another mutual fund within same company. How much unit of new mutual fund will I be having?
There is not enough information in the question to answer it exactly, but --
You can expect to have the same dollar value of shares in the post-merger mutual fund as you did in the pre-merger mutual fund. Exactly how many shares that is depends on the value of a share in the post-merger mutual fund at the time of the merge.
As an example -- you have 977 shares in mutual fund Alpha. They're each worth $1, so you have $977 total.
Bravo takes over Alpha.
If the value of a share in Bravo is $2, you will get 488.5 shares of Bravo -- still worth $977.
Taxes and the exact details of the merger could adjust this, but in the general case you'll wind up with exactly as much in the instant after the merger as you had in the instant before.