Final answer:
Impalpable means something that cannot be felt by touch or is subtly beyond the easy comprehension of the senses, which is best described as 'Not noticeable.'
Step-by-step explanation:
The word impalpable means something that cannot be felt by the touch or is difficult to grasp it mentally. It describes something that is not easily comprehensible or is too subtle to be touched or perceived by the senses. In the context of the options provided, the most accurate choice would be the (c) Not noticeable, as it conveys the concept of something that cannot be easily detected or experienced directly.