My question is for how many years the certification is valid.Oracle certifications never expire. They just slowly become irrelevant. I was one of the first OCPs in Oracle 7.3. That certification is still valid. However, no one cares.
Also is Oracle going to release a new version soon or 11g will be there for some time.Oracle 12c will be released sometime next year. That said, there are still numerous shops running Oracle 9i, and 10G was released in 2004. Oracle 11G will be around for many years. OE is unlikely to change the tests any time soon. Get the 11G certification and then take the 12c upgrade test when it becomes available.
Also would like to know difference between 10g and 11g (any web link ...please advice)There are a huge number. The 1Z0-050 test is all about the changes. The objective list is below which will give you some idea of the scope of changes: