Which of the following statements are correct?

$1.$ Isotopes are atoms with the same atomic number but different atomic mass.

$2.$ Isobars are atoms with the same number of neutrons but different atomic number.

$3.$ Isotones are atoms with the same mass number but different atomic number.

Select the correct answer using the codes given below.

Two atoms are said to be isotopes if _____.

Match the rule given in List I with the statement given in List II.
List I                                                List II

A. Pauli's exclusion principle         1. In orbitals of equivalent energy electron spins remain unpaired if possible

B. Hund's rule                                 2. Transition from the higher shell to K-shell

C. Lyman series                              3. The effect of magnetic field on the atomic spectra

D. Zeeman effect                            4. No two electrons can have the same four quantum numbers

Which of the following statements with regard to isotopes and isobars is/are correct?
$1.$ Isotopes have the same mass number.
$2.$ Isobars have the same atomic number.

Select the correct answer using the codes given below.