Question

Statement 1: Elements having same atomic number cannot have different mass numbers.
Statement 2: Atomic number depends on the number of neutrons.

• A. Only Statement 1 is true
• B. Only Statement 2 is true
• C. Both the statements are true
• D. Both the statements are false

Answer 1

The correct option is B

Only Statement 2 is true

Elements having same atomic number can have different mass numbers.

Some species have same number of protons but different number of neutrons. They are called isotopes.

Example: Isotopes of hydrogen.
$H_1^1$

$H_1^2$

$H_1^3$

As the number of neutrons changes, the mass number (neutrons + protons) changes. But the atomic number(no.of protons) remains the same.