Answer with another question.
Could God create a rock so heavy He could not lift it?"
Answer: This question is frequently asked by skeptics of God, the Bible, Christianity, etc. If God can create a rock that He cannot lift, then God is not omnipotent. If God cannot create a rock so heavy that He cannot lift it, then God is not omnipotent. According to this argument, omnipotence is self-contradictory. Therefore, God cannot be omnipotent. So, the question, could God create a rock so heavy He could not lift it? The quick answer is "No." But the explanation is far more important to understand than the answer...
This question is based on a popular misunderstanding about the definitions of words like "almighty" or "omnipotent." These terms do not mean that God can do anything. Rather, they describe the amount of God's power. Power is the ability to effect change - to make something happen. God (being unlimited) has unlimited power, and the Bible affirms this (Job 11:7-11, 37:23; 2 Corinthians 6:18; Revelation 4:8; etc.). Therefore, God can do whatever is possible to be done. God cannot, however, do that which is actually impossible. This is because true impossibility is not based on the amount of power one has, it is based on what is really possible. The truly impossible is not made possible by adding more power. Therefore, unless context indicates otherwise (e.g. Matthew 19:26 where man's ability is being shown in contrast to God's), impossibility means the same thing whether or not God is involved.
So, the first part of the question is based on a false idea - that God being almighty means that He can do anything. In fact, the Bible itself lists things God cannot do - like lie or deny Himself (Hebrews 6:18; 2 Timothy 2:13; Titus 1:2). The reason He cannot do these things is because of His nature and the nature of reality itself. God cannot do what is not actually possible to be done, like creating a two-sided triangle, or a married bachelor. Just because words can be strung together this way does not make the impossible possible - these things are contradictions, they are truly impossible in reality. Now, what about this rock? A rock would have to be infinitely large to defeat an infinite amount of lifting power. But an infinite rock is a contradiction since material objects cannot be infinite. Only God is infinite. There cannot be two infinites. So the question is actually asking if God can make a contradiction - which He cannot.
"Is there anything God cannot do?"
Answer: On a clear night, look up at the stars in the sky. Genesis 1 records that God made all of them! Imagine the power in just one star! But it is not just about raw power. There is intelligence and design packed in our universe down to the smallest DNA strand, down to the smallest subatomic particle. God’s power and wisdom are beyond our comprehension. That is why the LORD said to Abraham in Genesis 18:14, “Is anything too hard for the LORD?” That is why the LORD said to Moses when Moses questioned how God could possibly supply meat to several million Israelites in the wilderness, “Is the Lord’s arm too short?” (Numbers 11:23). That is why Jonathan told his armor bearer that the LORD didn’t need a lot of soldiers to get a victory (1 Samuel 14:6).
Jeremiah 32:17 states, “Ah Lord GOD! behold, thou hast made the heaven and the earth by thy great power and stretched out arm, and there is nothing too hard for thee.” Even in the spiritual realm, those that seem the farthest from salvation are not impossible for Him to reach (Mark 10:25-27). And as great as His power is, His love and mercy are just as great...even to the point of His willingness to send His own Son to die on the cross of Calvary to pay the penalty for a sinful mankind. He did this so that He, in complete justice, could forgive those who will turn away from self-reliance and sin to reliance upon Christ and His finished work. As parents, it would be far worse to see our children endure torment than go through it ourselves, and yet that is just what God the Father did. John 3:16, a familiar verse, states God’s great love: “For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.” This love was not just for the “good” people (there are none), but for us...a fallen, sinful, unlovely, rebellious people (Romans 3:10-23)...and yet He chose to shower us with His love (Romans 5:6-10) when we didn’t deserve it.
The only thing that God cannot do is act contrary to His own character and nature. For example, Titus 1:2 states that He cannot lie. Because He is holy (Isaiah 6:3; 1 Peter 1:16), He cannot sin. Because He is just, He cannot merely overlook sin. Because Christ paid the penalty for sin, He is now able to forgive those who will turn to Christ (Isaiah 53:1-12; Romans 3:26).