Thread safety object - static or not?

Question

I was recently in an interview and the tech guy asked me about how to make an application thread-safe.

Well, after explaining the lock() correctly, he s

Answer 1

If you have only one instance of a class that shares between multiple threads, it's ok to use normal object. but if you have multiple objects of a class that share between multiple threads, you have to use static object.

On the other hand, with normal object you can manage concurrency for one instance of a class and with static object you can manage concurrency in the scope of all instances of a class.