MCQs — Electrochemistry

Practice questions for Chemistry.

Question 61

In potassium dichromate (K2Cr2O7), given that potassium contributes +1 per atom (2 atoms) and oxygen contributes -2 per atom (7 atoms), the oxidation state of each chromium atom is:

A. +3

B. +4

C. +6

D. +7

Question 62

The general strategy for determining the oxidation number of an unknown atom in a compound is to:

A. Guess a value and check if it seems reasonable

B. Assign standard oxidation numbers to all other atoms first, then use the fact that the overall sum must equal zero (or the ion's charge) to solve for the unknown

C. Always assume the unknown atom has an oxidation number of zero

D. Look only at the compound's mass, ignoring its formula

Question 63

In boric acid (H3BO3), given that hydrogen contributes +1 per atom (3 atoms) and oxygen contributes -2 per atom (3 atoms), the oxidation state of boron is:

A. +1

B. +3

C. +5

D. -3

Question 64

Nitrogen dioxide (NO2) is a neutral molecule. Before finding nitrogen's oxidation state in it, you first need oxygen's standard oxidation number, which is:

A. -1

B. -2

C. +1

D. +2

Question 65

In nitric acid (HNO3), given that hydrogen contributes +1 and oxygen contributes -2 per atom (3 atoms), the oxidation state of nitrogen must be:

A. +3

B. +4

C. +5

D. +6

Question 66

Sulfur dioxide (SO2) is a gas commonly associated with air pollution and acid rain. In this neutral molecule, sulfur is recognized to have an oxidation state of:

A. +2

B. +4

C. +6

D. -2

Question 67

In sulfuric acid (H2SO4), given that hydrogen contributes +1 per atom (2 atoms) and oxygen contributes -2 per atom (4 atoms), the oxidation state of sulfur must be:

A. +2

B. +4

C. +6

D. +8

Question 68

In the sulfate ion (SO4^2-), given that oxygen contributes -2 per atom (4 atoms) and the ion's overall charge is -2, the oxidation state of sulfur must be:

A. +2

B. +4

C. +6

D. +8

Question 69

Before finding phosphorus's oxidation state in the phosphate ion (PO4^3-), you need oxygen's standard oxidation number, which is:

A. -1

B. -2

C. -3

D. -4

Question 70

In the ammonium ion (NH4+), given that hydrogen contributes +1 per atom (4 atoms) and the ion's overall charge is +1, the oxidation state of nitrogen must be:

A. +1

B. -1

C. -3

D. +3

Question 71

Nitrogen has an oxidation state of +4 in NO2 but +5 in HNO3. This illustrates that:

A. The oxidation state of a given element is fixed and identical in every compound it forms

B. The oxidation state of a given element can vary depending on the specific compound it is part of

C. Nitrogen never actually has a definite oxidation state

D. Oxygen's oxidation state changes between these two compounds

Question 72

Sulfur has an oxidation state of +4 in SO2 but +6 in both H2SO4 and the sulfate ion. This illustrates that:

A. Sulfur always has exactly the same oxidation state in every compound

B. Elements like sulfur can exhibit multiple different oxidation states across different compounds

C. Only metals can show more than one oxidation state

D. H2SO4 and SO4^2- must actually be the same substance

Question 73

Before solving for an unknown oxidation state in a compound, it is important to first assign oxidation numbers to:

A. Every atom simultaneously, using guesswork

B. The atoms whose oxidation states are already fixed/well known by the standard rules (such as oxygen, hydrogen, or Group IA/IIA metals)

C. Only the least electronegative atom present

D. None of the atoms; the unknown is solved first

Question 74

The strategy for determining the oxidation number of an atom in a neutral compound relies on the rule that:

A. The sum of all oxidation numbers in a neutral compound must equal zero

B. The sum of all oxidation numbers must always equal the number of atoms

C. Only metals contribute to the oxidation number sum

D. The compound's mass determines the oxidation numbers

Question 75

The strategy for determining the oxidation number of an atom in a polyatomic ion relies on the rule that:

A. The sum of all oxidation numbers in the ion must equal zero, regardless of the ion's charge

B. The sum of all oxidation numbers in the ion must equal the ion's overall charge

C. Only the central atom has a nonzero oxidation number

D. Oxidation numbers do not apply to ions

Question 76

To determine the formula of an ionic compound from ionic charges, you must find:

A. The largest possible ratio of cations to anions

B. The simplest whole-number ratio of cations to anions that results in a neutral compound

C. The atomic masses of the ions involved

D. The melting point of the resulting compound

Question 77

Ionic compounds are electrically neutral, meaning that:

A. They contain no ions at all

B. The total positive charge of the cations equals the total negative charge of the anions

C. They contain only cations

D. They contain only anions

Question 78

The first step in deriving an ionic compound's formula is to:

A. Balance the charges immediately without further information

B. Identify the ions present and their charges

C. Calculate the molar mass of the compound

D. Determine the compound's physical state

Question 79

The second step in deriving an ionic compound's formula is to:

A. Determine the ratio of charges needed to balance each other

B. Immediately write the final formula with no further checking

C. Look up the compound's common name

D. Measure the compound's density

Question 80

Calcium chloride requires two chloride ions for every calcium ion because:

A. Calcium forms a 2+ ion while chloride forms a 1- ion, so two 1- charges are needed to balance one 2+ charge

B. Calcium and chlorine always combine in a 1:1 ratio, with no exceptions

C. Chloride ions are always found in pairs in every compound

D. Calcium has no charge at all

🎯 How to get the most out of these questions

Attempt each question before revealing the answer.
Read the explanation even when you answered correctly — it reinforces the concept.
Note down any question you got wrong and revisit it the next day.
Use the pagination below the list to work through every page — do not stop at page 1.

📌 MCQs — FAQs

Are answers included for every question in this section?

Yes — each published question includes an answer. Explanations are shown where they have been added.

Can I print these questions?

Yes — use your browser's print option (Ctrl+P / Cmd+P) to print or save the page as PDF.

How often are questions updated?

New questions are added regularly. If a paper pattern changes, existing questions are reviewed and updated.