Question: I know this is not a technical related question.But i do not have any idea.I am going to develop a project which should be supported in both phone and tablet.Is it possible having one project working for both tablet and phone ?

Answer: 
Please, use MySQL.

There is almost no excuse to use Access backend. 

Like you said, Access has very poor connection abilities (every time the database is open, a connection is created as long as the program is still opened). Also, it has poor backup options (do you really want to make copies of the file every day?).

Also, Access has a "repair and compress database" option (for MDB, not sure about the newer format). It has a poor record of data consistency from what I experience with MDBs daily.

MySQL gives you a reliable data store, connections can be pooled properly, it has transaction support, and you can also run proper backups on it.

You can have a MySQL backend, and use Access forms as a frontend. I expect this should be a good enough compromise, and lets you scale it easily.
If you are the one that has to maintain the application also in future then drop the idea of Access and change into MySQL.
Access is only for personal use (or maybe with some small number of co-users)