When we move from left to right in transition elements, the decrease in atomic size is_due to intervening electrons.

Explanation

The decrease in atomic size when moving from left to right in transition elements is small due to intervening electrons. The atomic size of an atom is determined by the distance between the nucleus and the outermost electrons. In transition elements, the outermost electrons are the s electrons. As we move from left to right in the periodic table, the number of protons in the nucleus increases, but the number of s electrons remains the same. This means that the nuclear charge increases, which pulls the s electrons closer to the nucleus, resulting in a smaller atomic size. The intervening electrons, the d electrons, do not shield the s electrons very well from the nuclear charge. This is because the d electrons are located in a lower energy level than the s electrons. As a result, the increase in nuclear charge is not offset by the shielding effect of the d electrons, and the atomic size decreases. The decrease in atomic size is small in transition elements because the d electrons do provide some shielding effect. However, the shielding effect is not as strong as it would be if the d electrons were located in a higher energy level.