Question

in the compound mgo, what is the oxidation number of oxygen?
select one:
a. +4
b. +2
c. +1
d. -2

which of the following statements about polyatomic ions is false?
select one:
a. polyatomic ions act like a single atom.
b. each polyatomic ion has a single oxidation number.
c. polyatomic ions are found in nature.
d. polyatomic ions do not combine with ions of the opposite charge to form chemical compounds

Explanation:

Step1: Solve first question

MgO is a neutral compound, so total oxidation number is 0. Mg has oxidation number +2. Let oxidation number of O be $x$.
$+2 + x = 0$
$x = 0 - 2 = -2$

Step2: Solve second question

Analyze each option:

• a: Polyatomic ions act as a single charged unit, similar to a single ion/atom in reactions. True.
• b: Each polyatomic ion has a fixed overall oxidation number. True.
• c: Polyatomic ions like carbonate exist in nature. True.
• d: Polyatomic ions combine with opposite charges to form compounds (e.g., $Na_2CO_3$). False.

Answer:

1. d. -2
2. d. Polyatomic ions do not combine with ions of the opposite charge to form chemical compounds