(A) is true because the ionic radii goes on decreasing on moving left to right across a period as the nuclear charge goes on increasing from left to right. Thus, nucleus will hold the newly added electron more tightly. Hence ionic radii of alkaline earth metals is smaller than alkali metals. (R) is false because as the number of electron increases from left to right in a period and the atomic number also increases by a value of one. Therefore, alkaline earth metals have higher nuclear charge than the alkali metals.