(i) As we move from left to right in a period, the nuclear charge on an element increases but the number of energy shells remains the same. Due to increase in the nuclear charge, the force of attraction between nucleus and electrons increases. As a result, the size of the atom decreases on moving from left to right and therefore, results in decrease in the atomic radius in a period.
(ii) As we move from left to right, the nuclear charge on elements increased due to increase in the number of protons. With increase in the nuclear charge, the force with which the valence electrons are pulled becomes more stronger and becomes difficult for the atoms to lose the outermost electrons. Therefore, when we move from left to right in a period, the metallic character of the element decreases and non-metallic character increases.
(iii)Since the number of valence electrons remains same when moving from left to right in a group. So, there is no change in the valence and all elements in the same group have the same valency.
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