Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

It takes about one year for earth to orbit the sun.
Which of these takes about one year to complete?

Diffraction is the phenomenon in which light and sound waves become circular at the point source of a barrier.
What is the phenomenon in which light and sound waves become circular at the point source of a barrier?

Reactive elements are able to combine more easily with other elements.

Reactive elements are able to combine more what with other elements?