Answer:
The reaction that occurs is a redox reaction. The Copper metal (Cu 0)on the copper pennies is oxidized in concentrated nitric acid to produce Cu2+ ions. Copper is easily oxidized to Cu2+, which is blue in aqueous solutions (water) so you should see the solution turn blue as the copper penny reacts.
Have a nice day ;)(^-^)
Answer:
The wavelength the student should use is 700 nm.
Explanation:
Attached below you can find the diagram I found for this question elsewhere.
Because the idea is to minimize the interference of the Co⁺²(aq) species, we should <u>choose a wavelength in which its absorbance is minimum</u>.
At 400 nm Co⁺²(aq) shows no absorbance, however neither does Cu⁺²(aq). While at 700 nm Co⁺²(aq) shows no absorbance and Cu⁺²(aq) does.
Answer : The correct option is, (a) Synthesis
Explanation :
Synthesis reaction : A chemical reaction where multiple substances or reactants combine to form a single product.
It is represented as,

Combustion reaction : A chemical reaction in which a hydrocarbon react with the oxygen to give product as carbon dioxide and water.
It is represented as,

Single replacement reaction : A chemical reaction in which the more reactive element replace the less reactive element.
It is represented as,

In this reaction, A is more reactive element and B is less reactive element.
Double replacement reaction : It is a type of chemical reaction where a positive cation and a negative anion of two reactants exchange places to form two new products.
It is represented as,

(X and A are the cations, Y and B are the anions)
The given reaction is, 
In this reaction, calcium combine with the chloride to form calcium chloride as a product.
Hence, the given type of reaction is a synthesis reaction.
Answer:
5. gains two electrons.
Explanation:
In order to determine the most stable monoatomic ion of oxygen, we need to consider the octet rule: atoms will gain, lose or share electrons to complete their valence shell with 8 electrons.
Oxygen is in the Group 16 in the Periodic Table, so it has 6 valence electrons. Therefore, it will gain two electrons to have the electron configuration of the closest noble gas.