Which of these is a pure substance: sodium metal, solid sodium chloride, sodium chloride dissolved in water?

Pure substance is

a) sodium metal : it an element and it is pure substance

b) NaCl : it is an ionic compound and it is also a pure substance

c) NaCl dissolved in water : it is a homogeneous mixture of NaCl in water and hence it is not a pure substance

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

i don't know people like to fight everywhere rip.