How to drop only one thing in Minecraft?

When I press "Q" in Minecraft it drops the whole stack of items on Minecraft. If used to only drop only one item but just now when I clicked Q it dropped my whole stack. This is also happening to the backspace in Minecraft. When I type something and press backspace it deletes everything instead on one character. It is not my keyboard because I am typing with it right now and it is not deleting everything.

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