you have to set the TAB INDEX property of the option buttons. select the desired control and press F4 to open its properties,scroll down and find the tab index property. there you put the value. this value becomes the sequence number after which the focus will be moved to the desired control.
For example, if you set tab index of option1 to 0 and option 2 to 1, whenever you open the form the option 1 will be selected as default. then you can press tab to easily move the focus from option 1 to option 2. in the same way you can also set the tab index for other controls also.