Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have ?

Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Lithium atom has atomic mass 6 and has 3 protons in it nucleus. How many neutrons does it have? Write down its electronic configuration.

Which atom does not have any neutron in the nucleus and why?

(a) What is mean by (i) atomic number, and (ii) mass number, of an element ? Explain with the help of an example (b) What is the relation between the atomic number and mass number of an element ? (c) If an element M has mass number 24 and atomic number 12, how many neutrons does its atom contain ?

An atom of carbon has 6 protons. Its mass number is 12. How many neutrons are present in an atom of carbon ?

The atomic number of sodium is 11. How many protons are there in the nucleus of sodium atom ? How manu electrons does an atom of sodium contain ? How many electrons and protons does an ion of sodium which has a charge of +1 contain ?