The correct option is
E composure
'Equanimity' refers to Mr. Slope's calm mental state. Due to certain events listed in the passage, Mr. Slope's mental state was disturbed.
In general, 'equanimity' means a calm mental state, especially after a shock or a disappointment or in a difficult situation.
Option A - 'Status' means a state or condition at a particular time. However, it doesn't specify the 'mental state.' Thus option A is incorrect.
Option B - 'Happiness' means 'joy'. His happiness wasn't disturbed, his mental peace was. Thus option B is incorrect.
Option C - 'Justice' means fairness in the way people are dealt with. Thus option C is incorrect.
Option D - 'Complacency' is a feeling of uncritical satisfaction with oneself or one's achievements. Thus option D is incorrect.
Option E - 'Composure' is the state of being calm, or mental peace. As his mental peace was disturbed, we can use 'composure' here. Thus option E is the correct answer.
'Equanimity' - 'Composure'