Answer: The order with respect to
is 1.
Explanation:
Rate law says that rate of a reaction is directly proportional to the concentration of the reactants each raised to a stoichiometric coefficient determined experimentally called as order.

k= rate constant
x = order with respect to 
y = order with respect to A
n = x+y = Total order
From trial 1:
(1)
From trial 2:
(2)
Dividing 2 by 1 :
therefore x= 1
Thus order with respect to
is 1.
A physical change. chemical changes require the molecule itself to change. If you put NaCl into solution, the NaCl is still there which is evident by the fact that if you lower the amount of water, NaCl precipitates out.
Heat energy because combustion is an exothermic reaction.
It can be a compound or a single element. An element is a pure substance that cannot be separated into simpler substances by chemical or physical means. There are about 117 elements, butcarbon, hydrogen, nitrogen and oxygen are only a few that make up the largest portion of Earth.
I would say d.