题目

阅读理解After exactly a year of staying at home, we have adapted to socializing digitally, in short bursts of time. Remember in Before Times you could head to the gym after work and then get dressed for dinner and a night out? The pandemic(疫情) has changed this. Our social batteries have run out of charge. It's been a long time since we had to perform our social role for an extended period. For 23-year-old Hafsa, the excitement of her friends and family to restart their social lives has left her astonished. At the minute my parents are planning a trip abroad and I keep postponing getti在MgCl2、KCl、K2SO4三种盐的混合溶液中，若K+、Cl－各为1.5mol，Mg2+为0.5mol，则SO42－的物质的量为________．