ANS:C - abrasion resistance.

The M10 index of coke refers to its abrasion resistance. Coke is a porous, hard, and strong carbon material produced by heating coal in the absence of air to drive off volatile compounds. It is widely used in various industrial processes, including steelmaking, foundry casting, and chemical production. The M10 index is a measure of the abrasion resistance of coke and is determined through standardized testing methods. It represents the percentage of coke fines (particles passing through a specific sieve size) generated when a sample of coke is subjected to mechanical abrasion under specified conditions. A higher M10 index value indicates lower abrasion resistance, meaning that the coke sample is more prone to breaking down into fines when subjected to abrasion. Conversely, a lower M10 index value indicates higher abrasion resistance, meaning that the coke sample is more resistant to abrasion and produces fewer fines. Therefore, the M10 index provides valuable information about the durability and suitability of coke for various industrial applications where abrasion resistance is important, such as in blast furnaces, cupolas, and other high-temperature processes.