An element X, with atomic number Z and mass number A, is represented as ${}_{\mathrm{A}}{}^{\mathrm{Z}}\mathrm{X}$.

Q. An element along with its atomic number and mass number is represented as ${}_Z{X}^A$ where X is the symbol of the element, Z is the atomic number and A is the mass number. Represent elements A, B, C, D and E with its atomic number and mass number from the given data.

Elements	Number of protons	Number of electrons	Number of neutrons
A		x	y
B	a		b
C		m	m + 2
D		t	t
E	n		n + 1

Q. _____ number of protons are present in an element X with an atomic number Z and mass number A.

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