Which common solid substance is obtained in large quantities by evaporation of sea water in salt pans?

Introduction:
Many essential substances are obtained from natural sources through simple physical processes. This question checks whether the learner knows which everyday substance is produced on a large scale by evaporating sea water in specially prepared shallow basins, commonly known as salt pans.

Given Data / Assumptions:

• Sea water contains dissolved substances in it.
• Evaporation of sea water in salt pans leaves behind solid material.
• The options include common materials such as sugar, iron, salt, steel, and sand.

Concept / Approach:
Sea water is a solution, mainly of sodium chloride along with other salts. When sea water is allowed to stand in shallow basins, the sun heats the water and gradually evaporates it. As water changes to vapour, the dissolved salts remain behind and crystallise. This method is a classic example of using evaporation to separate a dissolved solid from a liquid. The solid obtained is common salt used in food and various industries.

Step-by-Step Solution:
Step 1: Recall that sea water tastes salty because of dissolved salts, mainly sodium chloride.Step 2: When sea water in shallow pans is exposed to sunlight and wind, water evaporates slowly.Step 3: As evaporation continues, the concentration of dissolved salts increases until they start forming crystals.Step 4: These crystals are collected, cleaned, and processed to form common salt.Step 5: Therefore, the substance obtained by evaporation of sea water is salt.

Verification / Alternative check:
Look at coastal regions where sea salt is produced. Photographs and documentaries clearly show large white crystals left behind after the water has dried up. People then collect this material as raw salt. No sugar or metal appears from sea water through this simple evaporation process. This visual evidence supports the scientific reasoning.

Why Other Options Are Wrong:
Sugar comes from sugarcane or sugar beet and is obtained through crushing, boiling, and crystallisation, not by evaporating sea water. Iron and steel are metals and alloys extracted from ores through complex processes in blast furnaces, not from sea water. Sand is formed from rock weathering and found on beaches and riverbeds, but it is not obtained by evaporating sea water in pans.

Common Pitfalls:
Some learners may confuse general sea side images of sand with salt, but sand remains on beaches regardless of sea water evaporation. Another mistake is to assume any solid near the sea must come from evaporation. The key is to understand that only dissolved substances can be recovered by evaporation, and the main dissolved solid in sea water is salt.

Final Answer:
Correct option: Salt