Answer:
A.
Explanation:
A decomposition reaction is when one reactant (the substances to the left of the arrow in the reaction) breaks apart into two or more products (the substances to the right of the arrow).
Because KClO3 is breaking down into KCl and O2, it's a decomposition reaction.
Answer:
Ammonia > Urea > Ammonium nitrate > Ammonium sulphate
Explanation:
Percentage by mass of nitrogen in NH3:
Molar mass of NH3= 17 g/mol
Hence % by mass = 14/17 × 100 = 82.35%
% by mass of NH4NO3
Molar mass of NH4NO3 = 80.043 g/mol
Hence; 28/80.043 × 100 = 34.98%
% by mass of (NH4)2SO4;
Molar mass of (NH4)2SO4= 132.14 g/mol
Hence; 28/132.14 × 100 = 21.19%
% by mass of CH4N2O
Molar mass of urea = 60.0553 g/mol
Hence 28/60.0553 × 100 = 46.62%
You should have given us a table, but I think my table shouldn't be too different.
Let's put oxidation numbers first.

You would have to know that Mg(s) is a reducing agent and Br2(l) is an oxidizing agent. But it is pretty common knowledge that the halogens will tend to take the electrons and alkali and alkaline earth metals will tend to give up electrons.
Mg is oxidized because it gives up electrons; Br2(l) is reduced because it gains electrons. Since the reaction conforms to what we would expect to <em>naturally</em> (thermodynamically favored) occur, it can take place given that the activation energy is supplied.
0.668 moles!
1 mole of Fe weighs 55.845 g.
1 mole has 6.02*10^23 atoms.
(4.02*10^23)/(6.02/10^23) = 4.02/6.02=2.01/3.01=0.668 moles