\which of the following statements is true?

elements in the last period are radioactive. a
atomic weight is the same as atomic mass. b
elements in the same group have the same number of electron shells. c
atomic number equals the number of neutrons in the nucleus of an atom. d

Elements in the last period are radioactive.

Explanation:

The first statement is true because,

The last period which is 7th period of periodic table consist of actinides and all these are radioactive.

The other options are incorrect because,

B= Atomic weight is the same as atomic mass.

Atomic weight is the average of the weight of the atoms of elements based on isotopic abundance, while atomic mass is the mass of single atom.

C = Elements in the same group have the same number of electron shells.

Elements in the same group have same number of valence electrons but electronic shell are different.

D= Atomic number equals the number of neutrons in the nucleus of an atom.

Atomic number is equal to the number of electrons or protons of an atom while sum of number of protons and neutrons are equal to the mass number.

i believe the answer is three water molecules