If you want to answer the question, you have to step outside the realm that Science explores...or make the argument that science doesn't "know" anything, that it is a set of theories that seem to work, but can be dropped in a second if a newer, better theory comes along.
Of course, if the teacher phrased the question as "...find something...", it implies a physical object, most of which can be explained by science (if not now, then sometime in the future). However, you can certainly make the argument that "Love" exists, though it is not a physical thing.
Outside the realm of science - metaphysics, religion, human consciousness are good areas to explore.
Why did the Big Bang happen? Not when, not what, not who, but WHY.
What is God?
What is Consciousness?
What does it mean to think?
(Turing Test)
What is Love?
Within the realm of science, go for the ignorance approach. Drop an apple on the teacher's desk, and announce "Science cannot explain an apple". To the astonished response, start asking questions:
What is the apple made of? Molecules, of course.
What are they made of? Atoms of course.
What are they made of? Electrons, Neutrons, and Protons, of course.
What are they made of? Well, Quarks as I understand the current theory.
Well, what are Quarks made of? Ummm...
You are at the point that theoretical physicists start getting a far-away look and start waving their hands to answer the question, and your teacher isn't going to be better.
Has Science explained the matter that makes up an apple? They certainly can't today, but as a valid (and hotly contested) field of endeavor, I have to believe that one day they will. If I were your teacher, I would argue that science CAN explain matter, and one day will - just not today.
/frank