_______ is the first and important step for preparing a temporary mount of a leaf peel to observe stomata.

Concept: The stomata are the small elliptical openings on leaves having chloroplasts.

The gas-exchanging processes such as respiration and photosynthesis are carried out with the help of small openings called stomata located on the leaves. Selecting a healthy leaf is the first and most important step for preparing the temporary mount of a leaf peel to observe stomata.

Hence, the correct answer is option B.