Some non-metals do not react with water, but react vigourously with air, like Phosphorous
Phosphorus is is very reactive nonmetal, If it is kept in open air,it reacts with oxygen and catches fire very easily
So it is kept in bottle of water as it does not react with water(as it is a non metal)
NCERT Question 3 (a) - Fill in the blanks :
(a) Phosphorus is very……………. non-metal.