Brass gets discoloured in air because of the presence of which of the following gases in air?
a. oxygen
b. hydrogen sulphide
c. carbon dioxide
d. nitrogen

Hydrogen sulphide

It is because the presence of mixture of hydrogen and sulphide and brass is a type of thing which has a color very light and mixture is non temperature (hot and cold type of temperature) so it gets discolored.

a community that experiences major changes undergoes progress

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products