Why do ships suffer a lot of damage from rusting despite being painted? 1. The entire hull of the ship remains above water level. 2. Water drops cling to the outer surface above water. 3. Sea water contains salts which slow down the process of rust formation. Select the correct answer using the code below:

The correct option is (b). Explanation Rusting is the corrosion of iron, a chemical process where iron reacts with atmospheric oxygen in the presence of water (or moisture) to form hydrated iron(III) oxide. The rate of this reaction is influenced by environmental conditions, particularly the presence of electrolytes. Statement-wise Analysis: - Statement 1 is Incorrect: Ships float due to buoyancy, which requires a significant portion of the hull to be submerged underwater. It is factually incorrect to state that the entire hull remains above the water level. - Statement 2 is Correct: The portion of the ship above the waterline is constantly exposed to sea spray and high humidity. Water drops clinging to the outer surface provide the moisture necessary for the oxidation reaction to occur. - Statement 3 is Incorrect: Sea water contains dissolved salts which act as electrolytes. These electrolytes increase the electrical conductivity of water, facilitating the movement of ions and thereby accelerating the electrochemical process of rusting. Salts do not slow down the process; they make it significantly faster compared to freshwater environments. Key Takeaway: The rusting of iron requires both oxygen and water. The presence of salt water accelerates this process because salts serve as electrolytes that enhance the rate of corrosion.

Why do ships suffer a lot of damage from rusting d... - NCERT Class 7 Science MCQ

Solution

The correct option is (b).

Explanation

Rusting is the corrosion of iron, a chemical process where iron reacts with atmospheric oxygen in the presence of water (or moisture) to form hydrated iron(III) oxide. The rate of this reaction is influenced by environmental conditions, particularly the presence of electrolytes.

Statement-wise Analysis:

Statement 1 is Incorrect: Ships float due to buoyancy, which requires a significant portion of the hull to be submerged underwater. It is factually incorrect to state that the entire hull remains above the water level.
Statement 2 is Correct: The portion of the ship above the waterline is constantly exposed to sea spray and high humidity. Water drops clinging to the outer surface provide the moisture necessary for the oxidation reaction to occur.
Statement 3 is Incorrect: Sea water contains dissolved salts which act as electrolytes. These electrolytes increase the electrical conductivity of water, facilitating the movement of ions and thereby accelerating the electrochemical process of rusting. Salts do not slow down the process; they make it significantly faster compared to freshwater environments.

Key Takeaway:
The rusting of iron requires both oxygen and water. The presence of salt water accelerates this process because salts serve as electrolytes that enhance the rate of corrosion.

NCERT Class 7 Science — Chapter 2: Physical and chemical changes

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