Which one is most resistant to decomposition by microbes in soil?

Answer: Option B

Lignin is the most resistant to decomposition by microbes in the soil. lignin after cellulose is the most abundant organic material on Earth, it decomposes very slowly.
The slow rate of lignin decomposition by fungi, actinomycetes, and bacteria is thought to be due to the complexity of its bonds and cross-linkages and because it has a relatively low nitrogen content. Soils with a loose structure allow for ample spaces between soil particles for oxygen to collect and in such soils, organic matter will decompose faster.