Which of the following is a good lubricant ?

Graphite powder is a highly effective solid lubricant due to its unique molecular structure. Unlike diamond, which is the hardest known substance and used for cutting or grinding [2], graphite is characterized as smooth and slippery [1]. Its low-friction properties arise from a layered crystal structure where carbon atoms are arranged in sheets with weak bonding between them, allowing the layers to slide over one another with minimal force. This makes graphite powder an ideal 'dry lubricant' for high-temperature applications, locks, and bearings where liquid oils cannot be used [5]. While petroleum-based products like paraffin and wax also serve as lubricants [3], graphite is specifically recognized as one of the two primary dry lubricants used in industrial machinery [5]. Alloys of carbon and iron, such as steel, are structural materials rather than lubricants.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Allotropes of carbon > p. 61
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Table 3.1 > p. 40
3. [5] https://en.wikipedia.org/wiki/Dry_lubricant
4. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 27: Fuel and Power > The uses of oil > p. 271