1. 工业中有着广泛的应用。近年来，我国科学家在分子筛研究领域不断取得新的突破。这些研究中涉及的部分元素在周期表中位置如下：                                                                                                                                                                                                                                                                                                                                                                                     

周期	族
	ⅠA	ⅡA	ⅢA	ⅣA	ⅤA	ⅥA	ⅦA
1	H
2				C	N	O
3	Na		Al	Si
4	K	Ca

将分子筛中的元素Na替换为K或Ca，可改变分子筛的孔径大小。这3种元素中（  ）