Which of the following statements is true? an element is made of only one type of atom. positively charged atoms have gained protons. a molecule must be made of two or more elements. electrons and neutrons are found in the nucleus of an atom.

The true statement is

An element is made of only one kind of atom.

Explanation:

An element is made of only one kind of atom. For example if we take element carbon it  is made of carbon atoms only .

The other atatements are false.

Positively charged atoms lose electrons and don't gain electrons.

A molecule can also be made of two or more  atoms of the same element. Eg H₂, P₄, Cl₂ etc.

Protons and neutrons are found in the nucleus of the atom and electrons are present outside the nucleus.

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c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.