What two actinides occur naturally on on Earth?

Answer 1

Uranium and thorium, i.e. #"U"# and #"Th"#.

Via a 5-second google search, one can find this info readily. Note that the "wrong" elements are bolded, so you have to be keen to see that thorium is the one that is naturally occurring, not plutonium.

Uranium can be found as ore deposits nearly everywhere on Earth. It is apparently about 40 times more common than silver and about 500 times more common than gold.

Thorium is typically found in the mineral monazite, but sometimes also in euxenite and thorianite.

#"Monazite (Ce)" ["(Ce, La, Nd, Th)PO"_4]:#

#"Euxenite-(Y)" ["(Y, Ca, Ce, U, Th)(Nb, Ta, Ti)"_2"O"_6]:#

#"Thorianite " ("ThO"_2):#

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Answer 2

Olivia Anton

Thorium and uranium are the two actinides that are found naturally on Earth.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.