4 NH3 + 5 O2 ---> 4 NO + 6 H2O How many grams NH3 are needed to form 11.2 liters of NO gas at STP?

molar mass NH3 = 17 g/mol

A 106.3
B 68
C n/a
D 8.5

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

  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-