Can someone help me please? Will mark brainliest Which of these statements is not true?

Select one:
a. Atoms of the same element can have different masses
b. The nucleus of an atom has a positive charge
c. Atoms of isotopes of an element have different numbers of protons
d. Atoms are mostly empty space

because of all the things that happen around the us, many people get into arguments which sadly could get physical, but we should actually make a change for that.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3