An atom has 9 electrons and 9 protons at the start. If it loses 2 electrons, the net charge on the atom will be __. If the atom instead gains 4 electrons, the net charge will be__.

A100-watt light bulb radiates energy at a rate of 100 j/s. (the watt, a unit of power or energy over time, is defined as 1 j/s.) if all of the light emitted has a wavelength of 525 nm , how many photons are emitted per second?

Asample of aluminum foil contains 8.60 × 1023 atoms. what is the mass of the foil?

What is the area in square meters of 448 g ai foil that has a thickness of 23921 nm? the density is 2.70 g/cm