What is the usual property of oxides of Group 3 and 4?

What is the number of moles of ‘He’ in 104 g of helium gas?

What is the mass number of an element, the atom of which contains two protons, two neutrons and two electrons?

Which one among the following is responsible for determining the chemical properties of an element ?

Which one of the following statements about the properties of neutrons is not correct?

What is the total number of naturally occurring elements?