When a grey coloured object made of metal A is left exposed to damp air for a considerable time, it gets covered with a red-brown flaky coating by the process called B which eats up the whole object gradually. It is said that the presence of C and D is necessary for this process to take place. If this object is galvanised by metal E, then the process B does not occur.
What is C?

Answer

To solve the question step by step, let's break down the information provided:

### Step 1: Identify Metal A
The question describes a grey-colored object made of metal A that gets covered with a red-brown flaky coating. Based on the video transcript, we learn that this metal A is Iron (Fe).

**Hint:** Look for the characteristics of the metal mentioned in the question to identify it.

### Step 2: Understand Process B
The red-brown flaky coating that forms on metal A (Iron) when exposed to damp air is known as rust. The process of rusting is referred to as Process B.

**Hint:** Think about common reactions that occur with metals when they are exposed to air and moisture.

### Step 3: Identify the Necessities for Process B
The transcript mentions that the presence of C and D is necessary for the process of rusting (B) to occur. Rusting requires both oxygen and water.

**Hint:** Consider what elements are typically involved in the corrosion of metals, particularly iron.

### Step 4: Determine C and D
Since the question asks specifically for C, we can conclude that C can be either oxygen (O2) or water (H2O). The other component, D, would then be the one not chosen for C. Therefore, C can be defined as oxygen.

**Hint:** Remember that rusting is a chemical reaction that requires both components; focus on the context of the question to determine which one to identify as C.

### Step 5: Understand the Role of Metal E
The question also mentions that if metal A (Iron) is galvanized with metal E, the process B (rusting) does not occur. The metal used for galvanization is zinc (Zn), which protects iron from rusting.

**Hint:** Think about methods used to prevent rusting in metals and what materials are commonly used for galvanization.

### Conclusion
To summarize, C is oxygen (O2), which is necessary for the rusting process to occur along with water (H2O).

### Final Answer
C is oxygen (O2).