Explanation:

Permaculture farming discourages monocultural practices but in conventional chemical farming, monoculture practices are pre-dominant.

Correct  Permaculture promotes polyculture or the cultivation of multiple crops in the same space, mimicking natural ecosystems. In contrast, conventional chemical farming often relies on monocultures, where large tracts of land are planted with a single crop, increasing the risk of pests and diseases.

Conventional chemical farming can cause an increase in soil salinity but the occurrence of such a phenomenon is not observed in permaculture farming.

Correct  Over-reliance on chemical fertilizers and pesticides in conventional farming can lead to soil degradation, including increased salinity. Permaculture focuses on building healthy soil and ecosystems without the use of chemicals, thus avoiding this issue.

Conventional chemical farming is easily possible in semi-arid regions but permaculture farming is not so easily possible in such regions.

InCorrect  Permaculture principles can be applied in various climates, including semi-arid regions. The key is designing systems in harmony with local conditions and resources. In fact, permaculture techniques can help improve water retention and soil health in such regions.

The practice of mulching is very important in permaculture farming but not necessarily so in conventional chemical farming.

Correct . Mulching is crucial in permaculture as it helps retain soil moisture, suppress weeds, and improve soil health. While mulching can also be used in conventional farming, it is not as central a practice as it is in permaculture.

Given this analysis, statements 1, 2, and 4 are correct