Question

define valency, atomic number,mass number​

Answer 1

Answer:

valency: the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.

atomic number: The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus.

mass number​: Mass number, in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom.

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