(b) Platinum, indium etc. are known as noble metals because they are ____towards many common reagents.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Noble Metals**: Noble metals are a group of metals that are resistant to corrosion and oxidation in moist air. They include metals like platinum, indium, gold, and others.

2. **Characteristics of Noble Metals**: Noble metals are characterized by their lack of reactivity towards many common reagents. This means they do not easily participate in chemical reactions with substances that would typically react with other metals.

3. **Examples of Reactions**: For instance, platinum (Pt) does not react with acids like hydrochloric acid or sulfuric acid under normal conditions. Similarly, indium (In) also shows limited reactivity with many common reagents.

4. **Conclusion**: Therefore, platinum, indium, and similar metals are known as noble metals because they are **inert** towards many common reagents.

5. **Final Answer**: Platinum, indium, etc. are known as noble metals because they are **inert** towards many common reagents.

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