Final answer:
Mendel's most significant conclusion was that traits are inherited in discrete units and not the result of blending. So, the correct answer is option b.
Step-by-step explanation:
Gregor Mendel's most significant conclusion from his experiments with pea plants was that traits are inherited in discrete units and are not the result of 'blending.' Mendel observed that when he crossed two pure-breeding pea plants with different characteristics, the first-generation offspring all looked like one of the parents, expressing the dominant trait. This led Mendel to propose the concept of dominant and recessive traits and the existence of discrete units of inheritance called genes.
So, the correct answer is option b.