Answer:2
Step-by-step explanation:
Weber's law of noticeable difference states that to observe a noticeable variation in sensory experience we need to increase the intensity beyond Difference threshold.
Here also for family reunion difference threshold is 5 onions so we need to add beyond it i.e. one onion more to get the noticeable change.
Thus for twice the chili with 10 potatoes we need to add 2 more.