It's a property of light called refraction. When light enters the water, it can't move as fast and it has to slow down slightly. It's kind of like how if you are walking, you can walk at a normal speed but if you walk in water, you can't walk quite as fast.
If light from the image enters the water straight, then the image looks normal - which was what you originally did when the pencil was straight up and down. If the light enters the water at an angle, then the change in speed between the open air and water causes the light beam to bend away from its original path. When the pencil was at an angle, the image was at a bigger angle in the water than in the air and made the pencil look like it was bent.
Why does a pencil look broken if you hold it at an angle in a beaker of water?
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It is ok
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