Mental weariness for want of occupation

Answer: Option B

One word substitute is Ennui.

Fatigue: extreme tiredness resulting from mental or physical exertion or illness.
Ennui: a feeling of listlessness and dissatisfaction arising from a lack of occupation or excitement.
Languor: tiredness or inactivity, especially when pleasurable.
Debility: physical weakness, especially as a result of illness.