Uncle Sam's rebus - Clue Eleven

Question

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After the easiness of the previous clue, you feel sure that the puzzles will start to get harder now. And the sign ahead seems to confirm that:

This is the last easy puzzle you'll get. After this, you'll really start to stretch your brain. But first, Uncle Sam has a rebus for you. Speak the answer, and proceed.

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Answer 1

I think its

Uranium

1:

"You" = U

2:

"Ray" = Ra

3:

"Knee" = Ni (Thanks @PartyHatPanda)

4:

"Umm?" = Um