What happens when milk is left at room temperature

it will change

Explanation:

if temperature of room is hot it doesn't freeze.

if temperature of room is cold it freezes

the milk may get oxidised. It causes bacteria to proliferate and eventually lower the pH. Thus, causing its sour taste and sometimes bad odour.

milk spoil because of growth of bacteria and formation of their metabolic byproducts. The bacterial group that can grow preferably well at room temperature are called mesophiles