Engineering Thermodynamics
In order that a cycle be reversible, following must be satisfied

When heat is being absorbed, temperature of hot source and working substance should be same
All of these
When beat is being rejected, temperature of cold source and working substance should be same
Free expansion or friction resisted expansion/compression process should not be encountered

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Engineering Thermodynamics
The specific heat at constant volume is

The amount of heat required to raise the temperature of unit mass of gas through one degree, at constant pressure
The amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume
Any one of the above
The amount of heat required to raise the temperature of 1 kg of water through one degree

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