Question

answers these question (science class 10)

Answer 1

1.Na and K catch fire bcoz they are most reactive and the reaction is highly exothermic so the heat produced and H2 gas makes it catch fire

3
Mg float bcoz MgSo4 are insoluble in water so the reaction stops there and the H2 evolved make it float on water

sorry for ques2 but I don't think tha Ca floats

Answer 2

Mg being a moderate reactive metal whent react with cold water results in formation of mgo which starts floating on water