does offline database reduces server load

I agree with Maciej Los here. It doesn't matter if the databases are unused.

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Will my queries run faster if i reduces number of online databases on server?

That depends. Depends on how many users are accessing/querying in your database hosted in the server. Depends on the query you sent.

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(i think more number of databases hosted on server , slower the server will be)

That also depends. Example: In server 1, you have 4 databases but 3 of them are unused, with 16 users accessing the database. In server 2, you have 2 databases, both of them are used, with 16 users accessing each database. What server do you think is slower?

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once i take database offline will it release some load on server?

What 'load' are we talking about? The workload or the space?

I think it's not important that the databases are unused. It's important how many place they occupy.

I would suggest you to shrink[^] the databases and detach[^] them to make a copies. After that remove detached databases from server (if they are really unused). You'll be able to attach them anytime you want.

Please, use Google with sentence: SQL Server perfomance fo further information.