What will happen when substances go through chemical changes

Which metal exist in liquid state and can be cut with knife ?

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.

Why does ammonia, nh3, behave as a base when it reacts with an acid? z