Assertion (A): Internal energy is a state function and extensive property.
Reason (R): Internal energy of a substance depends on gravitational force of attraction.
A. A and R are true and R is correct explanation of A
B. A and R are true and R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Hint: Internal energy is determined as the difference of initial and final stage. Internal energy depends upon the number of moles. Gravitational force depends on motion. Internal energy does not include energy of motion.

Complete step by step solution:
The thermodynamic properties which do not depend upon the path followed by the thermodynamic process are known as state properties. State property depends only upon the initial and final state of the system.
The properties which depend upon the amount of matter are known as extensive properties.
Internal energy only depends upon the initial and final state of the system, not on the path followed. So, the internal energy is a state function.
The internal energy depends upon the amount of matter. As more particles cause more collisions, so increase the internal energy. So, internal energy is extensive property.
S, the assertion (A) that internal energy is a state function and extensive property, is correct.
Internal energy is the intrinsic property of the system; it does not depend upon the gravitational force, so the internal energy of a substance depends on the gravitational force of attraction, is not correct.
Therefore, option (C) A is true, R is false, is correct.

Note: The thermodynamic properties which depend upon the path followed by the thermodynamic process are known as path properties. The properties which depend upon the amount of matter are known as extensive properties. The heat, heat capacity, and work only are the path functions; all thermodynamic properties are state functions. All forms of energy are state function.