Why is this the answer?

The answer is mirror because this is a very clever riddle that uses two main ideas to help you figure out the solution. The first part says, "If you drop me I'm sure to crack." This clue makes you think of something fragile, or something easily broken, which is often made of glass. If you accidentally drop a mirror, the glass surface will almost always crack into many pieces. This is the part of the riddle that describes a mirror's physical nature and how delicate it is. The second part gives you the biggest clue: "But give me a smile and I'll always smile back." What is the only thing you can look at that will copy your smile exactly and instantly? A mirror. When you stand in front of one and smile a big, happy smile, the mirror reflects your face and it looks like the mirror is smiling right back at you. It is a perfect copycat of whatever expression you make. The riddle plays a fun trick by pretending the mirror has feelings, like it is happy to see you smile. In reality, the mirror is just showing you a reflection of yourself. By putting the two clues together a fragile object that breaks when dropped, and something that perfectly copies your smile you can tell that the answer to this wonderful word puzzle must be a mirror. It is a tricky riddle that uses everyday things in a surprising way.