Assertion: The standard unit for expressing the mass of an atom is ‘u.’Reason: ‘u’ is also called unified mass

Step 1: Understand the assertion and reason. The assertion states that the standard unit for expressing the mass of an atom is 'u'. The reason given is that 'u' is also called unified mass.

Step 2: Evaluate the assertion. To evaluate the assertion, we need to determine if the statement is true or false.

Step 3: Verify the assertion. The standard unit for expressing the mass of an atom is not 'u'. The standard unit for expressing the mass of an atom is the atomic mass unit (amu).

Step 4: Evaluate the reason. The reason given is that 'u' is also called unified mass. However, this reason does not support the assertion because the standard unit for expressing the mass of an atom is not 'u'.

Step 5: Conclusion. Based on the evaluation of the assertion and reason, we can conclude that the assertion is false. The standard unit for expressing the mass of an atom is not 'u', but rather the atomic mass unit (amu).