The effective nuclear charge of an atom is primarily affected by

The effective nuclear charge (ENC) of an atom is affected primarily by inner electrons.

The net positive charge imparted to an electron of a polyelectronic atom is known as the effective nuclear charge (ENC).

The formula is:

,

Where = effective nuclear charge,

Z = nuclear charge, and

S = average number of electrons between the electron and the nucleus.

The outer electron has no influence on S since only the inner electron is counted.

Thus, Inner electrons would be responsible for primarily affecting the effective nuclear charge of an atom.

To learn more about effective nuclear charge, refer to the link:

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the dissolution of polymer can be thermodynamically described in 2 steps.