Final answer:
Uranus and Neptune are called "ice giants" due to their large quantities of 'ices' like water, ammonia, and methane. They have smaller hydrogen and helium envelopes and distinct internal temperatures and heat sources, differentiating them from the gas giants, Jupiter and Saturn.
Step-by-step explanation:
Uranus and Neptune are referred to as "ice giants" because their interiors contain more substances referred to as 'ices', such as water, ammonia, and methane, compared to their larger counterparts, Jupiter and Saturn, which are known as "gas giants." These 'ices' are in a form that includes both liquid and solid states due to the high pressures and temperatures within their cores. While Uranus and Neptune have atmospheres primarily composed of hydrogen and helium, they were less efficient than Jupiter and Saturn at attracting these lighter elements, leading to much smaller atmospheric envelopes relative to their core sizes. Moreover, Uranus and Neptune's internal heat sources differ; Neptune has a small internal energy source while Uranus does not emit a measurable amount of internal heat, contributing to the unique characteristics that set them apart from the gas giants.