X和Y是原子序数大于4的短周期元素,Xm+和Yn-两种离子的核外电子排布相同,下列说法中,正确的是( )
A:X的原子半径比Y小
B:X和Y的核电荷数之差为m-n
C:电负性:X>Y
D:第一电离能:X<Y
①埃克斯穿着人造纤维的衣服去拜访亲友
②爱丽丝与鲍勃谈恋爱不用面对面地进行
③李克尔梅在飞机上俯瞰美景
④摩尔根家族开始投资石油工业,获利丰厚
物质的性质决定其用途,请用相应物质的化学式填空.
(1)用于人工降雨 ____ ;
(2)形成化合物种类最多的 ____ ;
(3)用来制作肥皂____ .
When I entered the room, I found he was b____ in his work, so he didn't notice me come in.
Mary is looking forward to _____ from me , please remember_______ this letter on your way to school .