How are the subscripts determined when writing the formula for an ionic compound (ex. CaCl2)?

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

The kw for water at 0 °c is 0.12× 10–14 m2. calculate the ph of a neutral aqueous solution at 0 °c.

In general metals get as you move from left to right across the periodic table.