I can't fully answer this question because it is incomplete. In order for me to help you, I could just define what a precipitation reaction is and give a concrete example.
A precipitation reaction consists of two aqueous solutions that when reacted together, forms an insoluble salt. For example,
AgNO₃ (aq) + HCl (aq) --> AgCl (s) + HNO₃ (aq)
In this case, the precipitate is AgCl, Silver Chloride, which appears as a white solid.
The equation that shows the formation of chromium (ii) ion from neutral chromium atom is as follow
Cr ---> cr^2+ + 2e-
Cr^2+ is the chromium ion with oxidation state of two which is one of the common ion of chromium. Other common ion of chromium include chromium of oxidation state 6 and 3
Answer:

Explanation:
The hydrocarbon shown has a double bond. Hydrocarbons with double bonds are known as alkenes.
Cyclic alkanes have cyclic structure.
Alkanes only have single bonds.
Alkynes have triple bonds.
Answer:
Yes.
Explanation:
Zn2+ is the zinc ion in aqueous solution.
Zinc is a transition metal.
These metals are in the middle of the periodic table and have similar properties.
Given:
35.0 mL of acid with an unknown concentration
24.6 mL of 0.432 M base
Required:
Concentration of the acid
Solution:
M1V1 = M2V2
M1 (35.0 mL of acid)
= (0.432 M base) (24.6 mL
of base)
V1 = (0.432
M base) (24.6 mL of base) /
(35.0 mL of acid)
M1 = 0.304 M of acid