Answer:
A). The complementary shapes of an enzyme and a substrate.
Explanation:
The Lock-and-key mechanism was proposed by Emil Fischer for the first time and characterized as the metaphor which helps in elucidating the specificity of the enzymatic reactions. In this metaphor, the lock is described as the enzyme while 'key' is characterized as the substrate which the enzyme acts upon. If the key is not appropriately sized, it will not fit into the active site i.e. the keyhole of the lock or enzyme and reaction will not take place. Thus, <u>option A</u> is the correct answer.
Each of the organic compounds mentioned has a general formula so that we can identify the classification of a certain substance. The compound CH₃CH₂OH is an alcohol because it follows the general formula R-OH, where R is a hydrocarbon chain. In this case, the hydrocarbon chain is ethane. When a hydroxyl functional group is attached, it becomes an alcohol whose name is ethanol.
Answer: Among the listed substances 
is the molecular compound.
Explanation:
A chemical compound formed by the chemical combination of two or more non-metals is called a molecular compound or covalent compound.
For example, Xe and Cl are non-metals. The compound formed by them is which is a molecular compound.
A molecular compound is formed by sharing of atoms between the combining atoms.
Whereas NaF, 
and CaO are all ionic compounds as they are formed by chemical combination of a metal and a non-metal.
Thus, we can conclude that among the listed substances is the molecular compound.
Its a single Displacement reaction
