Force User To Choose Radio Options Before Submit?

I'm trying to write a shopping basket in ASP and I need to force the user to choose one or more "Option" radio button(s) before allowing the form to submit.

For example:

<input type="radio" name="option1" value="1">Red
<input type="radio" name="option1" value="2">Blue
<input type="radio" name="option1" value="3">Green
<input type="radio" name="option2" value="1">Small
<input type="radio" name="option2" value="2">Medium
<input type="radio" name="option2" value="3">Large

I want the user to HAVE to choose a colour and size from the above options before the form will submit or else they will get a Javascript popup message asking them to make a choice. (There may also be more/less options so it needs to be dynamic)

I know ASP inside out but very little knowledge of Javascript so once i have the basics of how to do it I can make the code dynamic. There will be a maximum of 5 "Options" for a product and a maximum of 6 choices for each Option.