I've seen this riddle or challenge to the reality of God's power a number of times over the years, including a mention somewhere today, so I figured I'd answer it since apparently a lot of people take it seriously. The riddle is "If God is all powerful, can he create something so heavy that he can't lift it up?"
The answer is "Yes he could, but it would not be real, it would be an illusion or lie. And since God is never untrue to his nature, he obviously would not do it as the creation would be bogus and not real, so it would be pointless and against his nature."
Let's break it down using logic. The question is bogus in the first place because it relies on a simple assumption that's just wrong. The question assumes, which most people don't realize, that God could ever be subject to the force of gravity. Um, duh. The reason something is heavy is that it has mass (it is an object made out of some material) and gravity is pulling on it. That's why something is heavy on earth (lots of gravity) yet on the International Space Station where there is very little gravity, astronauts can move huge "heavy" things with barely a finger tip.
So when you ask the question about God, it's a bogus set of assumptions since God is not comprised of any matter or energy, God does not reside in the 4 dimensional (3 dimensions plus time) world, and thus there is no part of God that is subject to gravity. God lives totally outside of the question.
So if he wanted to make you happy he'd have to create a robot or some other object made out of mass, put it in a gravity field, then give it something too heavy to lift AND, here's the problem, lie to you that this robot "is" Him. So obviously God can create any "test" scenario that a human comes up with, but he have to "humor you" to do so, and that means creating an illusion, to be polite, or lie to you. The Bible warns about testing God, that it's a really bad idea and not well received. But I know that many people ask this with genuine thoughtfulness, not realizing that the question itself is bogus.
It is human nature that humans always try to picture God as a living being that lives in a material/energy/time frame, and then can be "tested." Um, sorry, but God created the material universe by "standing" outside of it and obviously before the material world ever existed, since He created it! Any "ability" that people question about God is based on abilities that utilize matter, energy and time, all of which God created and exists totally outside of.
So it is not like God is "powerless" to create an illusion that you request, in other words, that a living body in the universe called "God" stands in a gravity field and can't lift something heavy. But obviously that is not really God because God lives outside of His creation and is pure spirit, no matter, no energy, no time sequence. With only a thought, a moment of His Will, God can do absolutely anything with his creation (the universe) or those he created in the pure spirit place of heaven (the angels) or outside of heaven (hell). He could make this universe disappear in a second, if he wanted to. He could make and label any human or animal "God" and then make it stand in gravity and be unable to lift something. But there IS no matter or energy, and thus no gravity or other forces, or ticking of a clock of sequence of actions, in heaven where God is God.
People who ask this question to erode faith and mock God demonstrate that they don't even have a sixth grade knowledge of either science or God. However, I understand that many folks, especially young people (Hi!) ask this riddle sincerely, because you've not received the how-to about using logic to answer questions and identify fallacious assumptions (bogus premises).
Hope this helps!