why control box(minimize , maximise and close button) is not accessible in design time in vb.net or there is another method to activate these tools.

They are properties of the main form. For example look in properties for MinimizeBox and set it to either True or False. Change ControlBox property then see what happens to your program.

It might help to change the properties sorting to alphabetical then you can more easily find controlbox, maximizebox and minimizebox.

thanks for reply
but i didn't mean that what you replied.
i want to use these three button in design time but what you say is just belong to something happening with form in runtime.

you can think of my problem as :- if you want to maximize the form in design time(not in run time) so you have to scale the form width of height using mouse dragging(i.e. can't maximize directly), so any ideas to activate these three buttons in design time.

hope i explained the problem clearly . . .

You have a couple of options.
1 - When you click on the form, on the right edge and bottom edge you will see little white squares these are for changing the size by dragging the mouse cursor. You aren't restricted to the visible area of the IDE. You can drag it to the full size of the screen. Scroll bars will automatically appear so you can change which part of the form is visible.

2 - With AutoSize set to False, use the Size property to manually set the form to a specific size.

I don't think that is possible, you can only change their properties. They are not functional during design.

ok , so we can't do that in design time .
yes i know that we can chage these properties but these will not make any sense while designing the form.

Doing some low level programming you could remove them, but I don't know how.
You could play with the FormBorderStyle property to change how the form looks, during design.