A student constructs a cold pack which becomes cold to the touch when activated. The cold pack is activated when an inner water pouch is squeezed until it bursts, allowing the water to mix with a solid substance. She constructs the device as shown below. The solid she uses in the cold pack is ammonium chloride. She wants to modify her device to make it colder when it is activated. She conducts some tests and collects the data shown below. Based on the test results, which solid should she use that would best modify her cold pack?