is it possible to encrypt the sd card folder r not please help me
Only by modifying the operating system and creating your own custom ROM.
not possible , let me know what can i do for folder security in android sdcard
If your objective is to allow the user to defend against other people stealing the user's data, you can encrypt individual files as part of how you store them. For example, you could use SQLCipher for Android to encrypt a SQLite database that you put on external storage.
If your objective is to hide data from the user, that is implausible. Your encryption algorithm and key will be in your app, which anyone can examine and use to get at the encrypted data. If you do not want users having access to certain pieces of data, do not put that data on the user's device.