In order for the reaction 2Al(s) + 6HCl(aq) →2AlCl3(aq) + 3H2(g) to occur, which of the following must be true? a. Al must be above Cl on the activity series.
b. Al must be above H on the activity series.
c. Heat must be supplied for the reaction.
d. AlCl3 must be a precipitate.

Option b) Al must be above H on the activity series.

may be this is the right answer .

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

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