1.

A metal (M) burns with dazzling brilliance in air to give a white powder.The white powder reacts with water to form a white precipitate and a colourless gas with a characteristic smell.The metal (M) decomposes hot water but not cold water, liberating the inflammable hydrogen gas. The metal (M) is:

Answer»

K
Ca
Mg
Rb

Solution :HYDROGEN is LIBERATED when Mg reacts with hot water. Rb, K and Ca gives hydrogen gas even with COLD water.
`Mg+O_2toMgO , Mg+N_2toMg_3N_2`
`Mg_3N_2+6H_2O to 3MG(OH)_2 + 2NH_3 uarr`
`Mg+2H_2O("hot")toMg(OH)_2+H_2`


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