The negation of the statement

“Plants take in CO₂ and give out O₂” is

If the statement is p then its negation is ~p, it means if p is true then ~p is false and vice versa.

p: Plants take in CO₂ and give out O₂

q: Plants take in CO₂

~q: Plants do not take in CO₂

r: Plants give out O₂

~r: Plants do not give out O₂

Now,

~(qᴧr)=~q V ~r

Hence, Plants do not take in CO₂ or do not give out O₂.