The figure shows the \((P\text-V)\) diagram of an ideal gas undergoing a change of state from \(A\) to \(B.\) Four different paths \(\mathrm{I, II, III}\) and \(\mathrm{IV},\) as shown in the figure, may lead to the same change of state.
                  

(a) The change in internal energy is the same in cases \(\mathrm{IV}\) and \(\mathrm{III}\) but not in cases \(\mathrm{I}\) and \(\mathrm{II}.\)
(b) The change in internal energy is the same in all four cases.
(c) The work done is maximum in case \(\mathrm{I}.\)
(d) The work done is minimum in case \(\mathrm{II}.\)

 Which of the following options contains only correct statements?

1. (b), (c), (d) 2. (a), (d)
3. (b), (c) 4. (a), (c), (d)
Hint: The internal energy is a path-dependent variable.
 
Step 1: Find the change in internal energy.
The change in internal energy for the process \(A\) to \(B,\) is given by;
\({dU}_{{A} \rightarrow {~B}}={nC}_{{V}} {dT}={nC}_{{V}}\left({~T}_{{B}}-{T}_{{A}}\right)\)
which depends only on temperatures at \(A\) and \(B.\)
 
Step 2: Find the work done.
The work done for \(A\) to \(B,\) is given by;
\({dW}_{{A} \rightarrow {~B}}=\text { Area under the }{P}\text-{V} \text {curve which is maximum for the path } \mathrm{I} \text {. }\)
Hence, option (3) is the correct answer.