An atom of element has there subatomic particles namely, proton, electron and neutron. Here, for a neutral atom, number of proton is equal to number of electron (this is not in the case of ions), this is equal to atomic number of an atom. In an atom, nucleus contains protons and neutrons which is responsible for mass of the atom and electrons move around nucleus in fixed orbits. Thus, atomic mass of an atom is equal to sum of number of protons and neutrons.
Option (b): Proton is the particle in nucleus of an atom, whose total number is equal to atomic number of that atom.
(4) Option (b): Atoms of same element have same atomic number because mass number can be different for different isotopes of atom. Since, atomic number is equal to number of protons, thus, number of protons are same for all atoms of the same element.
(5) Option (d): Isotopes are defined as atoms of same element with same atomic number but different mass number. Thus, correct option is (d) mass numbers.
Answer : The excess reactant in the combustion of methane in opem atmosphere is 
molecule.
Solution : Given,
Mass of methane = 23 g
Molar mass of methane = 16.04 g/mole
The Net balanced chemical reaction for combustion of methane is,
First we have to calculate the moles of methane.
= 
= 1.434 moles
From the above chemical reaction, we conclude that
1 mole of methane react with the 2 moles of oxygen
and 1.434 moles of methane react to give 
moles of oxygen
The Moles of oxygen = 2.868 moles
Now we conclude that the moles of oxygen are more than the moles of methane.
Therefore, the excess reactant in the combustion of methane in open atmosphere is molecule.
Answer:
I think
(d) All compounds contain the same elements in the same properties
