Why is this the answer?

The answer is voice because it is the most amazing "instrument" you carry with you every single day. The riddle is a clever word puzzle that helps us see how special our own voice really is. Let us look at the first clue: "What instrument can make any sound". Think about all the noises you can make with your mouth and throat. You can sing a cheerful song, whisper a secret, shout for joy, or even make funny sounds like a chirping bird or a silly elephant. A real musical instrument, like a trumpet or a piano, can only make certain sounds. But your voice is so flexible it can make almost any sound you can imagine! You can change your voice to sound happy, sad, or excited, and you can even practice to sound like a cartoon character or a silly monster. Because it can do all these different things, your voice is called a universal instrument. The next part of the riddle holds the best secret: "and be heard, but not touched or seen?" When you talk, what is actually happening? First, you take a big breath of air. Then, that air moves from your lungs, past two tiny flaps of skin in your throat called vocal cords, and out of your mouth. As the air rushes past, those tiny cords vibrate very quickly. This movement makes waves of sound, and those waves travel to your friend's ear, so they can hear your words. Because the voice is just a vibration of air, it means it is completely invisible, or something you cannot "see." It does not have a color or a shape, like a toy or a piece of fruit. And since the voice is not a solid object, you cannot reach out and "touch" it, even though you can feel the warmth of your breath when you speak close to your hand. It is amazing how such a powerful thing can be completely unseen. It is a tool for sharing all your ideas and feelings with the whole world. So, your voice is a perfect match for the riddle. It is an instrument that is always with you, it makes all kinds of noise, and it is a wonderful secret that can be heard by everyone but never seen or touched. It truly is your most important and powerful tool for communication.