Mango showers are pre-monsoon rainfall found primarily in Kerala and coastal Karnataka- Correct.
Mango showers are indeed pre-monsoon showers that are particularly common in Kerala and coastal Karnataka. They occur during the late summer or early monsoon season and are beneficial for the ripening of mangoes and other early crops.
Nor'westers are beneficial for rice cultivation in Assam- Correct.
Nor'westers (also known as Kal Baisakhi in West Bengal) are thunderstorms that occur in eastern India, including Assam and West Bengal, during the pre-monsoon season. These storms bring significant rainfall, which is beneficial for the sowing of the summer rice crop (also known as Aus rice) in Assam.
Loo winds bring significant moisture to the Northern Plains - Incorrect.
Loo winds are hot, dry, and strong westerly winds that blow during the summer season over the Northern Plains of India. They are characterized by their high temperature and low humidity. Therefore, they do not bring significant moisture; in fact, they contribute to the dryness of the region.