Which statement concerning elements is true? (1) different elements must have different numbers of isotopes. (2) different elements must have different numbers of neutrons. (3) all atoms of a given element must have the same mass number. (4) all atoms ofa given element must have the same atomic number

The statement concerning chemical elements which is true is: (4) All atoms of a given element must have the same atomic number.

In Science, an atom can be defined as the smallest unit composed of matter that forms all chemical elements. Thus, atoms are fundamental building blocks of matter and determines (defines) the structure of all chemical elements.

Generally, atoms comprises three distinct particles and these are:

The number of protons found in the nucleus of an atom is referred to as atomic number and it is the same for all atoms of a specific chemical element.

In conclusion, all atoms of a particular chemical element must have the same number of protons or atomic number.

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the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

i think   the answer is c hope i'm right