Which type of change must occur to form a compound? (1) chemical (3) nuclear (2) physical (4) phase?

Let's go through each of the answers and think about why they work or don't work.

Chemical forms compounds.

Nuclear changes the element completely. We're going to use the sun as an example. The sun is in a state of plasma. It's really hot and has all these particles hitting into each other. The nucleus' of atoms are hitting into each other forming larger elements. It's real crazy. Nuclear is not correct.

Physical cannot form a compound.