1. Shielding effect is effective, when orbitals in the inner shells are completely filled. So, statement (1) is correct. 2. Inner shells are show effect. So, statement 2 is incorrect. 3. Shielding effect as well as ionisation energy decrease down the group. So, statement 3 is incorrect. 4. With increase in nuclear charge, shielding effect decreases. So, statement 4 is incorrect.