Answer:

Explanation:
In a single-displacement reaction, one element exchanges partners with another element in a compound.

This is a single-displacement reaction, because the element Fe exchanges partners with H in HCl.

This is not a single-displacement reaction, because it is a reaction between two compounds.
This is a double displacement reaction in which the K⁺ and H⁺ cations change partners with the anions.

This is not a single-displacement reaction. It is another double displacement reaction, in which the Na⁺ and H⁺ cations change partners with the anions.

This is a single-displacement reaction, because the element Ca exchanges partners with H in H₂O.
are not single-displacement reactions.
If by classical you mean formula name it is CrPO4<span>.</span>
Answer: The oxidation number of Cu decreased
Explanation: In Cu2O equation Cu has an oxidation number of
Cu+1 O-2
then in the product side Cu is represented as a single element.
The rule on oxidation number for an individual element is always O
So Cu has 0 oxidation number.
Answer: This is because the number of shell increases .
Explanation: On moving from left to write on the periodic table the reactivity of non metals increases because number of shells increases and the force with which the nucleus hold electrons decreases.