This is simply 4.3*10^0. First, note the power of 10: Since the largest digit is in the units place, the power of 10 is 10^0. Then, we round to two significant digits, resulting in 4.3*10^0.
The number of protons in the nucleus of the atom is equal to the atomic number. So the number of atomic number is equal to the number of protons. hope it helped (:
