Q1: Which of the following is not a suitable solid lubricant ?

ANS:D - None of these

"None of these" indicates that all of the options listed – talc, molybdenum disulfide, and graphite – are suitable solid lubricants. Here's a brief explanation:

1. Talc: While talc is not as commonly used as molybdenum disulfide or graphite, it does possess lubricating properties and can be used as a solid lubricant in certain applications, especially in situations where lower friction levels are acceptable.
2. Molybdenum disulfide: Molybdenum disulfide, also known as MoS2, is a well-established solid lubricant known for its excellent lubricating properties, even in high-temperature and high-pressure environments. It forms a low-friction film between surfaces, reducing wear and friction.
3. Graphite: Graphite is another widely used solid lubricant due to its ability to provide effective lubrication in various conditions, including high temperatures and in the presence of corrosive substances. Graphite forms thin layers between surfaces, allowing them to slide over each other smoothly.