How many atoms of hydrogen are in an ice cube with a mass of 15.5 g?

Which type of orbits are found in the principal energy level n = 2 a - s b - s, f c - s, d d - s, p e - s, p, d

How many moles of lead are in 1.50 x 10^12 atoms of lead? could you explain the answer as well and not just give it to me i am refreshing for finals and i need to know how to do it

What is the percent by mass of magnesium sulfate in mgso4.7h2o