Is there a one way hakone free pass

I will be Travelling from Tokyo to hakone and staying there for 3D2N. After hakone I will travel to Kyoto, would like to know if there's a hakone free pass from Tokyo to hakone then Kyoto or there a one way free pass from Tokyo to Hakone.

Secondly, for the free pass is it based on 24hours or per day? If I'm going there for 3D2N how many days free pass should I buy?

You can buy Hakone Free pass without roundtrip fare ticket in Odawara, it will costs you 4000 yen. But yeah, it will be more expensive if you add Odakyu Romance Car, which cost around 2080 yen.

There are two types of Hakone free pass, 2-day and 3-day. Since you will spend 3D2N, you should take the later one since it only cost you around 500 yen more than the 2-day pass.

This is that you had to find first.
http://www.hakonenavi.jp/english/freepass/

Get the three day pass without the train leg from Tokyo. Then you have much more choice. Romance Car is one of the more expensive options. You can travel to Odawara on the regular train for 880yen.

So the better choice will be just buying the round trip hakone pass?

So the better choice will be just buying the round trip hakone pass?

If I'm going there for 3D2N how many days free pass should I buy?

Whether a transportation pass pays off or not depends on your itinerary.
How do you plan to travel in Hakone?
Where in Hakone would you stay overnight?

You seem to have not yet read the following article on this Japan Guide website.
- Hakone Free Pass (Hakone Freepass)
http://www.japan-guide.com/e/e2358_008.html

A Hakone Freepass allows you to travel freely
inside the designated area beyond Odawara Station
by most major public transportation modes (other than taxi) which are available to Hakone visitors.
There is a version which is valid just inside the area.

You can pay the Odakyu regular basic fare (plus, Limited Express surcharge if you take a Romancecar train) to go until Odawara Station then purchase there the above-mentioned version of Hakone Freepass.
: 880 yen paid in cash (or 874 yen paid with a PASMO Card or a Suica Card) as basic fare to go from Shinjuku Station to Odawara Station.
: 890 yen paid as Limited Express surcharge if you take a Romancecar train.
: 4000 yen | 4500 yen paid for 2-day | 3-day Hakone Freepass.

for the free pass is it based on 24hours or per day?

Per day.
The validity term of Hakone Freepass is counted by calendar days, which is common among most major transportation passes in Japan.
(You can tell the difference by name; a pass which is good for one or a few times of 24 hours is sold under a name like Tokyo Subway 48-hour ticket.)

Is there a one way Hakone free pass

There is not a version designed for a one-way trip to Odawara and a trip inside the designated area.

There is a version which can be used to travel by Odakyu lines from a certain station (e.g. Shinjuku Station) to Odawara Station and back; it does not cover Limited Express surcharge.

Logically you can choose this version to travel from Shinjuku to Odawara then renounce your right to travel back with it; however that is not cost-wise good because the gap in the prices of the two versions, which is 1140 yen, is larger than the regular one-way basic fare for this section.

You can buy Hakone Free pass without roundtrip fare ticket in Odawara