Shallow copy by using Memberwiseclone() method

class Test:ICloneable
{
    int a;

    Test()
    {  
        a = 20;
    }

    public int Data
    {
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        {
            a= value;
        }
    }

    object Clone()
    {
        this.MemeberWiseClone();
    }
}

Test a = new Test();
Test b = a;

Now, if we modify the data a, b also changes

Question 1:

When the assignment happens which function is called, is the MemberwiseClone() of the System.object called

Question 2:

Test a = new Test();
Test b = (Test) a.Clone();

If you change the data of a , b doesn't change, it is because of the shallow copy.

Does MemberwiseClone() creates new object and then does a copy?

Writing b = a changes b to refer to the same object that a refers to.
Note that this is only true for classes; if a and b are structs, the value will be copied.

The MemberwiseClone method returns a new object and assigns all of the fields in the new object to refer to the values from the original object.
That's a shallow copy.

From MSDN:

The MemberwiseClone method creates a shallow copy by creating a new object, and then copying the nonstatic fields of the current object to the new object. If a field is a value type, a bit-by-bit copy of the field is performed. If a field is a reference type, the reference is copied but the referred object is not; therefore, the original object and its clone refer to the same object.

MemberwiseClone() creates a shallow copy, this has nothing to do with the assignment you do here though:

Test a = new Test();
Test b = a;

Both object references (a and b) point to the same object now. If you need MemberwiseClone() you have to call it directly, just as you do in your Clone() method.