How many significant figures are in these numbers

How many moles are contained in 5.6 l of h2 at stp

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium

The plant food contains nh4)3po4 what tests would you run to verify the presence of the nh4 ion and the po4 ion