It’s e 2.0 x 10^-4 because it is a fraction
Choice-B is the correct one.
-- The atomic number is the number of protons in the nucleus.
-- Each proton in the nucleus is usually matched by one electron in the 'cloud'.
-- The addition of a proton OR a neutron increases the mass number by 1 .
-- Electrons have such small mass that they don't figure into the atomic mass at all.
-- Volume . . . made out of 3 dimensions of length
-- Density . . . made out of mass, and 3 dimensions of length
-- Area . . . made out of 2 dimensions of length
-- Acceleration . . . made out of length and time
<em>Mass</em> is not made out of anything else. It's fundamental. A few other fundamental things are length, time, and electric charge.
