Practice questions without fighting the page.

<b>Answer: D. Exosphere</b> <ul> <li><b>Reason:</b> Exosphere is the outermost layer of Earth's atmosphere, gradually blending into space at high altitudes (roughly 700–10,000 km).</li> <li><b>Key concept:</b> Atmospheric layering includes troposphere, stratosphere, mesosphere, thermosphere, and exosphere; the exosphere marks the boundary with space.</li> <li><b>Tip:</b> No sharp end to layers; transitions are gradual.</li> <li><b>Why others are incorrect:</b> Stratosphere is below, Mesosphere is middle, Ionosphere is a region within the upper atmosphere/thermosphere with ionized particles, not the outermost layer.</li> </ul>

<b>Correct option: D</b> <ul> <li><b>Argon</b> is an inert gas, belonging to the noble gases group with a complete outer electron shell, making it chemically very unreactive under normal conditions.</li> <li>Key concept: inert gases have stable electron configurations (noble gas configuration) and form few or no compounds.</li> <li>Why others are not inert: <ul> <li>Hydrogen can react to form many compounds (H2, acids, hydrocarbons).</li> <li>Nitrogen, though relatively unreactive, forms N2 and can react under certain conditions (fertilizers, explosives).</li> <li>Oxygen is highly reactive and supports combustion.</li> </ul> </li> <li>Exam tip: recall “noble gases” (He, Ne, Ar, Kr, Xe, Rn) as the truly inert ones.</li> </ul>