Word Choice – Using ‘True’ vs ‘Truth’ in a Sentence

You want to exchange the item you purchased. That is, you want to return to the store the one you bought and have the store give you a new one for one reason or another.

You want the store to replace it.

The clearest way to express this in American English is to say to the salesperson or service desk person:

I'd like to exchange this rug for a larger one (because it's too small for the space I want to put it in). [NB: The reason is optional unless you're asked for a reason.]

I'd like to exchange this space heater for a new one that works. When I tried to use this one that I bought here yesterday, it didn't work. Can we test the new one here before I take it home?

"Government" is an attributive noun, "governmental" is an adjective. They mean the same thing, and I believe you can use either word whenever you want. That said, I do believe "government" is a little more commonplace, but that may differ depending on the phrase.

For example, I think "government official" is probably more commonplace than "governmental official," at least in modern English. Another example: I've seen "governmental bodies" many times. In formal English, you might see "governmental" more often.

Ultimately, I think it doesn't matter which you use, but it might be a good idea to pick one and be consistent with it.