Question

When a popcorn kernel heats up, the moisture inside turns to steam, building pressure against the hard, starchy outer surface (the hull). This internal pressure becomes immense. Eventually, the hull gives way, and the kernel explodes. As it explodes, the soft starch inside becomes inflated and bursts, turning the kernel inside out to form the familiar white fluff.
The pop sound itself is a complex phenomenon. It does not occur at the precise moment the hull ruptures. Rather, researchers have found the sound occurs just after the initial burst, when the super-heated water vapor is suddenly released, creating a rapid expansion of gas. This sudden pressure drop creates empty cavities within the forming structure and generates the distinct sound wave. This acoustical phenomenon is similar to the sound produced by a miniature geyser erupting, or a champagne cork popping.

Which choice best describes the relationship between the "pop" sound and the physical transformation of the kernel, as presented in the second paragraph?
A) The sound precedes the visual change, signaling the immediate onset of the kernel's expansion.
B) The sound is a byproduct of the starches inflating, rather than the initial hull failure.
C) The sound and the hull's rupture happen simultaneously as the internal pressure reaches its maximum threshold.
D) The sound is a secondary effect resulting from the rapid atmospheric displacement caused by the escaping steam.

Answer 1

D) The sound is a secondary effect resulting from the rapid atmospheric displacement caused by the escaping steam.

Explanation: the paragraph states the pop occurs just after the hull ruptures, when super‑heated vapor is suddenly released and rapidly expands, producing pressure changes and cavities that generate the sound.