Corrosion and its prevention — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Corrosion of a metal is best described as

• A. the gradual deterioration of the metal by chemical or electrochemical reaction with its environment
• B. the melting of a metal on heating
• C. the mechanical breaking of a metal under stress
• D. the purification of a metal by electrolysis

Question 2 · difficulty L2 · understanding

Rusting of iron requires the presence of

• A. oxygen only
• B. water only
• C. both oxygen and water
• D. carbon dioxide only

Question 3 · difficulty L2 · understanding

Which method protects iron by coating it with zinc?

• A. Galvanisation
• B. Electrorefining
• C. Distillation
• D. Annealing

Question 4 · difficulty L2 · understanding

Why can zinc protect iron even if the zinc coating is locally scratched?

• A. Zinc is less reactive than iron
• B. Zinc is more easily oxidised than iron and acts sacrificially
• C. Zinc prevents all contact with water even at the scratch
• D. Iron becomes chemically inert in contact with zinc

Question 5 · difficulty L3 · application

Which metal is most suitable for sacrificial protection of an iron pipeline?

• A. Copper
• B. Silver
• C. Magnesium
• D. Gold

Question 6 · difficulty L3 · application

Iron is in electrical contact with copper in moist air. Which metal is more likely to corrode preferentially?

• A. Copper
• B. Iron
• C. Both at exactly the same rate
• D. Neither

Question 7 · difficulty L3 · application

Painting an iron surface prevents corrosion mainly because the paint

• A. raises the melting point of iron
• B. acts as a barrier separating iron from air and moisture
• C. converts iron into a noble metal
• D. removes all electrons from the surface

Question 8 · difficulty L3 · application

In cathodic protection, the metal structure to be protected is made the

• A. anode
• B. cathode
• C. electrolyte
• D. salt bridge

Question 9 · difficulty L4 · application

An iron sheet is coated separately with zinc and with tin. If both coatings are scratched to expose iron, which statement is most accurate?

• A. Both coatings protect equally by sacrificial action
• B. Zinc can still protect iron sacrificially, whereas tin may accelerate local iron corrosion
• C. Tin protects sacrificially but zinc does not
• D. Neither coating affects corrosion after scratching

Question 10 · difficulty L4 · application

A steel water tank is connected to a block of magnesium. After some time the magnesium block loses mass. What is the best explanation?

• A. Magnesium acts as the cathode and is reduced
• B. Magnesium acts as a sacrificial anode and is oxidised instead of the steel
• C. Steel dissolves and plates onto magnesium
• D. Magnesium prevents oxygen from dissolving in water