Consider the following statements:
a) the entropy of an isolated system never decreases.
b) heat never flows spontaneously from cold to hot.
c) the total thermal energy of an isolated system is constant.
which of these express the second law of thermodynamics?
1. a only
2. b only
3. c only
4. both a and b
5. both b and c

1. A only

Explanation:

First law of thermodynamics it sates that energy of the universe is constant.It is also known as energy conservation law.

Therefore according to the first law of thermodynamics ,the thermal energy of the system is unchanged.

Second law of thermodynamics states that ,it is impossible to make a device which take heat from higher temperature energy resource and give 100 % work without heat rejecting.

Therefore only option A is correct.

1. A only

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

at right angles to each other