A chemical element (X) is represented by ${}_Z{X}^A$. If ‘X’ is any element, then what do ‘A’ and ‘Z’ stand for?

Q. Any chemical element (X) can be represented as ${}_Z{X}^A$ where ‘Z’ is the atomic number and ‘A’ is the mass number. The atomic number refers to the number of protons and the mass number refers to the sum of protons and neutrons in an atom. For an element, calcium which has 20 protons and 20 neutrons, identify the correct representation:

Q. An element is represented by ${}_Z{X}^A$, where Z is atomic number which is also equal to number of proton, A is mass number and X is symbol of the element.
Mass number (A) = Number of protons (Z) + Number of neutrons.
Isotopes: Atoms having same number of proton
Isobar: Elements having same mass number
Isotones: Elements having same number of neutron (A-Z)

The sum of the number of electrons, protons and neutrons in the three isotopes ${(}^{16}O{,}^{17}O{,}^{18}O)$ of oxygen is:

Q. Any chemical element (X) can be represented as ${}_Z{X}^A$ where ‘Z’ is an atomic number and ‘A’ is the mass number. For an element, calcium which has 20 protons and 20 neutrons, identify the correct representation.

Q. An element is represented by ${}_Z{X}^A$, where Z is atomic number which is also equal to number of proton, A is mass number and X is symbol of the element.
Mass number (A) = Number of protons (Z) + Number of neutrons.
Isotopes: Atoms having same number of proton
Isobar: Elements having same mass number
Isotones: Elements having same number of neutron (A-Z)

An isotone of ${}_{40}^{90}Zr$ is _________.

Q. An element is represented by ${}_Z{X}^A$, where Z is atomic number which is also equal to number of proton, A is mass number and X is symbol of the element.
Mass number (A) = Number of protons (Z) + Number of neutrons.
Isoelectronic: Species/ elements having same number of electron
Isodiaphers: Elements having same value of $|(A-2Z)|$
Isotopes: Atoms having same number of proton

Which of the following is a pair of isodiaphers?