Question

What causes shielding effect to remain constant?

Answer 1

I think U are taking about D block elements as u might know effect shielding due to s>p>d>f
then in d block as u got from right to left

1. electrons get added in penultimate shell of the d block elements
   penultimate i.e. second last shell
   explanation as 4s is the outershells most as 2 electrons get added already as you are moving electrons are added to d shell which can accommodate the electrons fro 1 to 10

2. As getting added these shows increasing shielding for the incoming electrons i.e size must grow but now nuclear charge is also increasing i.e attraction to incoming electrons or the outermost shell electrons

3. When these shielding due to d shell is equal to nuclear attraction i.e repulsion is equal to attraction size in constant