Plastids are easily observed under a microscope because:

Correct option is B

The correct answer is (b) they are large and contain pigments

Explanation:

• Plastids are important, double-membrane bound cellular organelles found exclusively in the cells of plants and algae.
• They act as significantly large structures relative to many other internal cellular organelles, making them visually prominent.
• Most distinctly, certain types of plastids rigidly contain vividly coloured chemicals known as pigments (like chlorophyll).
• These natural pigments dramatically enhance their visual contrast, rendering them extremely easy to locate and observe vividly under standard light microscopes without heavy artificial staining.

• The most well-known plastids are chloroplasts, which uniquely contain the green pigment chlorophyll and are heavily responsible for photosynthesis.
• Chromoplasts contain vibrant pigments (like carotenes and xanthophylls) offering distinctive colors strictly to flowers and maturing fruits.
• Leucoplasts are largely colorless storage plastids explicitly handling the internal storage of starch, essential oils, and protein granules.

• Being extremely small naturally hinders microscopic observation. Plastids are relatively large cellular organelles, which contradict this description.

• While plastids uniquely hold their own distinct circular DNA and ribosomes, DNA is fundamentally sub-microscopic and physically invisible under a basic light microscope.

• Only leucoplasts inherently lack pigments. Because they lack contrast-enhancing colors, they are significantly harder to observe precisely than their pigmented counterparts.