Question

a tamper - resistant receptacle has a safety device that prevents the insertion of a(n)
a plug for an appliance that is switched on
b appliance plug
c item into the hot or neutral slot
d ungrounded plug

Explanation:

Tamper - resistant receptacles are designed to prevent foreign objects (other than proper appliance plugs) from being inserted. An ungrounded plug (which is not a standard, safe plug for most modern applications in terms of proper connection and safety in a tamper - resistant context) is what the safety device in a tamper - resistant receptacle is meant to block. Appliance plugs (standard ones) are supposed to be inserted. Plugging an appliance that is switched on is about the operation of the appliance, not about what is prevented from insertion. Inserting an item into the hot or neutral slot is dangerous, but the main prevention is of ungrounded (improper, non - standard in terms of safety and proper fit in many cases) plugs.

Answer:

D. ungrounded plug