Answer:
The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts using copper salts as reagents or catalysts. It is an example of a radical-nucleophilic aromatic substitution.
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.
The next test would be the lime water test.
Explanation:
If placing the gas in lime water will turn the solution milky, then the gas is most probably carbon dioxide, the lime water (Ca(OH)₂) turns milky due to the formation of solid CaCO₃ that is insoluble after reaction with carbon dioxide.
Carbon dioxide also puts out the flame in the splint test because it does not support combustion.
Answer: Oxidation is defined as the reaction in which there is loss of electrons. It is accompanied by increase in oxidation number.
Zinc in solid state has oxidation number of zero and on losing electrons changes to 
with oxidation number of +2.
Reduction is defined as the reaction in which there is gain of electrons. It is accompanied by decrease in oxidation number.
Hydrogen ions with +1 oxidation state gains electrons and converts to molecular hydrogen with oxidation state of zero.
In the given redox reaction, both oxidation and reduction takes place. They go hand in hand.
Zinc converts to and gets oxidized. 
gains electron and convert to 
.
