Why turning fork have two legs?

Why that shape like "Y" ?

Please anyone clear my doubts
Why should the tuning fork have two prongs?

Good question. Clearly a single metal bar will produce a tone when struck and the frequency of a tuning fork is a function of the single tine length. I have two theories about why two tines are used:
1: The tines resonate together in such a way as to prolong the duration of the sound.
2: A single tine will create a sound of amplitude A and so n tines will create a sound of amplitude nA. Maybe two tines makes a reasonably loud enough sound without being too large for easy manipulation.

I hope someone else comes and puts their own two cents in because I'm not very certain about my answers!

If you just used a straight rod, and held it in your hand, your hand would damp out the vibrations. A tuning fork has a handle you can hold without disrupting the vibrations. I think there may be other reasons too. Something to do with vibration modes perhaps.

Hi asterisk_man,
single tine will create a sound of amplitude A and so n tines will create a sound of amplitude nA. Maybe two tines makes a reasonably loud enough sound without being too large for easy manipulation
I thing your this idea is wrong, because we hit one side of turning fork’s prong, so that energy is distributed 2 prong.

When we hit the tuning fork we make on of the legs vibrate, as Kesavan said. Then, I think, the air trapped between the two legs of the fork is contracted and expanded rapidly. This helps to apply a force on the other leg as well and within some moments two legs resonate at the same frequency creating a good sound.

kesavan, you're certainly right that the energy will be distributed across 2 prongs. I think I had some additional complication in mind when I wrote that but I can't remember it now.

Another idea I had was that somehow the fork isolates the vibration from the handle but this is clearly not true because there is often mention of holding a tuning fork against a box of some kind to allow it to become even louder.