Answer should be 1,2,3. Gibberellin induces flowering in LDP under short day condition by replacing the long day requirement. It speeds up the malting process in brewing industry by enhancing the function of enzyme α-amylase, which catalyzes the malting process, i.e, conversion of Cereal Starch into maltose.

Gibberellin and its effects

1. Gibberellins can substitute light treatment.
Gibberellins are a group of plant hormones that play a crucial role in various physiological processes, including seed germination, stem elongation, flowering, and fruit development. However, they do not have the ability to substitute light treatment. Light is an essential environmental factor that plants require for photosynthesis and other light-dependent processes. Gibberellins cannot replace the role of light in providing energy for plants and promoting photosynthesis. Therefore, statement 1 is incorrect.

2. Gibberellins increase the yield of malt from barley grain in the brewing industry.
Gibberellins have been extensively used in the brewing industry to increase the yield of malt from barley grain. Malt production involves the germination of barley seeds, and gibberellins promote the elongation of barley stems, leading to increased malt yield. By applying gibberellins during malting, the growth and development of barley grains can be enhanced, resulting in higher malt production. Therefore, statement 2 is correct.

3. Gibberellins favor flowering in long-day plants.
Gibberellins do not specifically favor flowering in long-day plants. The initiation and regulation of flowering are complex processes influenced by various factors, including photoperiod (day length), temperature, and hormonal signaling. Long-day plants require a certain duration of light exposure to flower, but gibberellins alone do not solely determine flowering in these plants. Gibberellins can interact with other hormones and environmental factors to influence flowering, but their role is not restricted to long-day plants. Therefore, statement 3 is incorrect.

4. Gibberellins induce apical dominance.
Apical dominance refers to the inhibition of lateral bud growth by the dominant apical bud. Gibberellins play a crucial role in releasing or breaking apical dominance. They promote the elongation of stems and inhibit the development of lateral buds, allowing the apical bud to grow uninhibited. However, it is important to note that other hormones, such as auxins, also contribute to the regulation of apical dominance. Therefore, statement 4 is correct.

In summary, the correct statements are:
- Gibberellins increase the yield of malt from barley grain in the brewing industry.
- Gibberellins induce apical dominance.

However, it should be noted that gibberellins cannot substitute light treatment, and their role in flowering is not specific to long-day plants.