Question

The atoms of same element having same atomic number but different mass are called:
A.Atomic number
B.Mass number
C.Isotopes
D.Isobar

Answer 1

Hint: Isotopes: The elements which have the same atomic number but different atomic mass, are known as isotopes.
Isobars: The elements which have the same atomic mass but different atomic number, are known as isobars.

Complete step by step answer:
 First of all let us talk about elements, atoms, mass number and atomic number.
Atoms: It is the smallest unit of an element. The elements are made of the same kind of atoms. In the atoms there are three particles: electrons, protons and neutrons.
Electrons: They are the negatively charged particle having negligible mass. They move in the atoms outside the nucleus in a fixed orbit.
Protons: They are positively charged particles. They have mass. They are present in the nucleus (a special room in the atoms were neutrons and protons are present).
Neutrons: They have no charge but they have mass. They are also present in the nucleus along with protons.
Gram molecule: It is defined as the number of grams of the substance i.e. the molecular mass of the substance.
Atomic mass: It is defined as the total number of protons and neutrons present in the nucleus of an atom. It is represented by symbol A.
Atomic number: It is defined as the number of protons in the nucleus of an atom. It is represented by symbol Z.
Isotopes: The elements which have the same atomic number but different atomic mass, are known as isotopes. For example: carbon$ - 12$ and carbon$ - 14$. In both the carbons the atomic number is the same i.e. six but they have different atomic mass i.e. carbon$ - 12$ the mass is $12$ and for carbon$ - 14$ the mass is $14$.
Isobars: The elements which have the same atomic mass but different atomic number, are known as isobars. For example: Argon and calcium. They both have atomic mass $40$ but atomic number of argon is $18$ and atomic number of calcium is $20$.

So, the correct answer is Option C.

Note:
Isotones: The elements which have the same number of neutrons, but different number of electrons and protons, are known as isotones. For example: boron$ - 12$ and carbon$ - 13$. They both have seven neutrons in their atoms.