Online Test — Chemical Reactions and Equations
18 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 18
easy
The number written in front of a formula in an equation is called a:
subscript
coefficient
valency
state symbol
Explanation: The big number in front of a formula is the coefficient; it is used to balance equations.
Question 2 of 18
easy
A balanced chemical equation is consistent with the law of:
conservation of charge only
conservation of mass
definite volumes
constant temperature
Explanation: Equal atoms on both sides reflect that mass is conserved.
Question 3 of 18
medium
The correctly balanced form of CH4 + O2 → CO2 + H2O is:
CH4 + O2 → CO2 + H2O
CH4 + 2O2 → CO2 + 2H2O
2CH4 + O2 → CO2 + 2H2O
CH4 + O2 → 2CO2 + H2O
Explanation: CH₄ + 2O₂ → CO₂ + 2H₂O has 1 C, 4 H and 4 O on each side.
Question 4 of 18
easy
Which state symbol stands for 'dissolved in water'?
(s)
(l)
(g)
(aq)
Explanation: (aq) means aqueous — dissolved in water.
Question 5 of 18
medium
We must NOT balance an equation by:
adding coefficients
changing subscripts in a formula
checking atom counts
writing correct formulae
Explanation: Changing a subscript changes the substance; only coefficients may be adjusted.
Question 6 of 18
easy
Burning of magnesium ribbon in air is an example of a:
decomposition reaction
combination reaction
displacement reaction
double displacement reaction
Explanation: Magnesium combines with oxygen to form a single product, MgO — a combination reaction.
Question 7 of 18
easy
CaCO3 → CaO + CO2 on heating is a:
combination reaction
thermal decomposition reaction
displacement reaction
neutralisation reaction
Explanation: A single compound breaks down on heating — thermal decomposition.
Question 8 of 18
medium
2AgCl → 2Ag + Cl2 in sunlight is used in:
whitewashing
black-and-white photography
galvanisation
neutralisation
Explanation: This photolytic decomposition of silver chloride is the basis of black-and-white photography.
Question 9 of 18
easy
Fe + CuSO4 → FeSO4 + Cu is a:
combination reaction
decomposition reaction
displacement reaction
double displacement reaction
Explanation: More reactive iron displaces less reactive copper from its salt.
Question 10 of 18
medium
Mixing Pb(NO3)2 and KI solutions gives a yellow precipitate of:
KNO3
PbI2
PbO
I2
Explanation: Lead iodide, PbI₂, is insoluble and appears as a yellow precipitate.
Question 11 of 18
medium
The reaction HCl + NaOH → NaCl + H2O is best classified as:
combination
displacement
double displacement (neutralisation)
decomposition
Explanation: An acid and base exchange ions to form salt and water — a double displacement (neutralisation).
Question 12 of 18
medium
Decomposition reactions generally:
release energy
absorb energy
need no energy
are always explosive
Explanation: Breaking a compound apart requires energy, so these reactions are usually endothermic.
Question 13 of 18
easy
Oxidation is defined as the:
loss of oxygen
gain of oxygen or loss of hydrogen
gain of hydrogen
loss of electrons only
Explanation: At the Class 10 level, oxidation is gain of oxygen or loss of hydrogen.
Question 14 of 18
medium
In CuO + H2 → Cu + H2O, the substance reduced is:
H2
CuO
Cu
H2O
Explanation: CuO loses oxygen and becomes Cu, so it is reduced.
Question 15 of 18
easy
Rusting of iron is a process of:
reduction
oxidation
neutralisation
sublimation
Explanation: Iron gains oxygen from the air, so rusting is an oxidation (redox) process.
Question 16 of 18
easy
Both conditions required for iron to rust are:
heat and light
oxygen and water
acid and base
nitrogen and water
Explanation: Rusting needs both oxygen (air) and water (moisture).
Question 17 of 18
easy
Galvanisation protects iron by coating it with:
tin
zinc
copper
carbon
Explanation: Galvanisation is coating iron or steel with a layer of zinc.
Question 18 of 18
medium
Rancidity in fried food is caused by the:
reduction of fats
oxidation of fats and oils
rusting of the container
decomposition of water
Explanation: Rancidity is the oxidation of fats and oils, giving a bad smell and taste.