To determine the most appropriate answer for the given assertion and reason, let us analyze both statements separately:

Assertion A:

12-20% acrylamide in PAGE restricts the migration of large molecules.

Polyacrylamide Gel Electrophoresis (PAGE) is a method widely used in biochemistry and molecular biology to separate proteins, or nucleic acids, based on their size. The concentration of acrylamide in the gel affects pore size:

• A higher acrylamide concentration (such as 12-20%) results in a gel with smaller pores.
• These smaller pores hinder the movement of larger molecules, effectively restricting their migration.

Thus, Assertion A is correct.

Reason R:

Pore size of the gel affects the separation of molecules.

In gel electrophoresis, the separation of molecules is greatly influenced by the pore size of the gel. Smaller pores will restrict the movement of larger molecules, while allowing smaller molecules to pass through more easily. This principle helps in the effective separation of molecules based on size.

Therefore, Reason R is also correct.

Combining Both Statements:

Both Assertion A and Reason R are correct, and Reason R logically explains why Assertion A is correct. The pore size, influenced by the acrylamide concentration, directly impacts the migration of molecules during PAGE.

Conclusion:

The correct answer is: Both A and R are correct and R is the correct explanation of A.