Is construction give it a/an + verb rather more formal or rather more informal?
Examples.
“Give it a stir” instead of “Stir it”
“Give it a slice” instead of “Slice it”
“Give it a shake” instead of “Shake it” etc.

Question

Answer

I would say that they are the same. Other uses for this, which are idioms are "give it a whirl" (try it), "give it a go" (also try it). Also "give it a chance", "give it a look"- there are many uses for this construction. They are slightly informal but certainly not vulgar.

Answer

Your first and third examples work because they're commonly used with "give it...", and the meaning is clear either way. But if you say "give it a slice", it sounds like you're giving a slice of something to an animal.

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