Which duty has been violated in the following scenario?

Your agent has been instructed to sell your goods for $$400$ per pound. Your agent has heard of a new business that is willing to pay $$500$ per pound but since you told the agent to sell at $$400$ they do so$.$ You find out later that your agent knew of the $$500$ per pound price.

a$.$ duty of diligence

b$.$ duty of good conduct

c$.$ duty of obedience

d$.$ duty to inform

e$.$ duty to account