For a seed to germinate successfully, several conditions must be met. Let's evaluate the given factors:
(A) Viability of seed: This is absolutely essential. A seed must be alive, meaning its embryo is capable of growth and development. A non-viable (dead) seed cannot germinate. So, (A) is true.
(B) Proper environment: This is also essential. Seeds require suitable environmental conditions for germination, which typically include adequate moisture (water), appropriate temperature, and oxygen. Some seeds also have specific light requirements. So, (B) is true.
(C) Seed free from dormancy: This is essential. Dormancy is a state where a viable seed will not germinate even if provided with favorable environmental conditions. The dormancy must be broken (naturally or artificially) for germination to occur. So, (C) is true.
(D) Thin seed coat: This is not universally essential for germination. While a very thick or impermeable seed coat can impose dormancy (physical dormancy) and prevent water uptake or gas exchange, many viable, non-dormant seeds with moderately thick seed coats germinate perfectly well. A thin seed coat might facilitate faster germination in some cases but is not a fundamental requirement for all seeds to germinate. Some seeds require scarification (abrading the seed coat) if it's too hard, but that relates to overcoming dormancy, not an essential feature of all germinable seeds.
Therefore, the essential factors for germination from the list are viability, proper environment, and freedom from dormancy.
This corresponds to option (3).
(A), (B) and (C) only