In diplontic life cycle the diploid sporophyte is dominant. Fucus are algae which has diplontic life cycle.
So, the correct answer is option 'A'.

Fucus Life Cycle

The correct answer is option 'A', Fucus exhibits a diplontic life cycle.

Diplontic Life Cycle
- In a diplontic life cycle, the dominant phase is the diploid (2n) phase, which is the sporophyte.
- The diploid sporophyte produces haploid (n) spores through meiosis.
- The haploid spores germinate and develop into haploid gametophytes.
- The gametophytes produce gametes (eggs and sperm) through mitosis.
- Fertilization occurs when the sperm and egg fuse to form a diploid zygote.
- The zygote develops into a new diploid sporophyte, completing the life cycle.

Fucus Life Cycle
1. The Fucus life cycle starts with the release of haploid (n) zoospores from the diploid (2n) sporophyte.
2. These zoospores are flagellated and swim in water.
3. The zoospores settle on a suitable substrate and germinate, forming haploid (n) male and female gametophytes.
4. The male gametophytes produce non-flagellated sperm, while the female gametophytes produce eggs.
5. The sperm are released into the water and swim towards the eggs.
6. Fertilization occurs when a sperm fuses with an egg, forming a diploid (2n) zygote.
7. The zygote develops into a diploid sporophyte, which remains attached to the substrate.
8. The diploid sporophyte grows and produces structures called receptacles, which contain conceptacles.
9. Conceptacles are specialized structures that house gametangia, where gametes are produced.
10. The diploid sporophyte produces diploid (2n) zoospores within the conceptacles.
11. These zoospores are released and settle on a substrate, starting the cycle again.

Summary
- Fucus exhibits a diplontic life cycle, where the dominant phase is the diploid sporophyte.
- Haploid zoospores are released from the sporophyte and develop into haploid gametophytes.
- The gametophytes produce gametes, which undergo fertilization to form diploid zygotes.
- The zygotes develop into new diploid sporophytes, completing the life cycle.