Question: Does static methods and class are good for scalability ? I think so static class/method improves scalability of application and instance methods doesn't scales much. So is it good programming practice to write static method where ever it is possible ?

Answer: 
I think you're barking up the wrong tree:

In the real world, scalability (or the lack thereof) typically springs from appropriateness of one's algorithms and the efficiency of the operations made against data stores (think: good SQL queries).

Things like whether a method is static or not (or the % of methods which are static) generally have nothing to do with the scalability of a system. You can certainly have a super scalable system which uses no static methods, or super scalable system which uses them exclusively.
Voted down. The OP clearly doesn't quite understand OO. An instance method doesn't take up any extra space when an instance object is created. Static methods aren't going to save you anything unless you're also avoiding creating any instances, in which case you're going so far afield from what an OO language was built for that it's sort of pointless discussion.