On many common appliances, there is an “O” or “I” on the power switch. What does each symbol mean?

"I" symbol means the current goes through the system (imagine the 'I' being a line, like a circuit connecting [power to the device]) "O" symbol means the current does not go through the system. ( the circle is an open circuit, having no power flowing through it

Write the formula of the compound.
Write the numbers of each atom in the formula. Insert the relative atomic mass for each type of atom. Calculate the total mass for each element.
Add up the total mass for the compound.