<h2>Answer to Q21.</h2>
<u>The correct option is Rocks become less dense when they melt
</u>
<h2>Explanation:</h2>
The density of rocks get less when they are in molten form. Density is equal to mass per volume so in solid form the volume is reduced but when the volume increases in liquid form the density decreases that is why we can say that in molten form rocks have less density.
<h2>Answer to Q23. </h2>
<u>The correct option is D. </u><u>convergent oceanic-continental plate boundary
</u>
<h2>Explanation:</h2>
When oceanic crust comes closer to continental crust, the denser oceanic plate plunges beneath the continental plate which is a process called subduction. This process occurs at the oceanic trenches inside the ocean. The rocks inside them melt and produce magma which is a hot material and then this magma rises and erupts, creating volcanoes. The yellow stone national park is associated with the same formation of tectonic phenomenon.
<h2>Answer to Q24.</h2>
<u>The earth's rigid outer layer, consisting of the crust and uppermost mantle, is called the </u><u>Lithosphere</u>
<h2>Explanation:</h2>
The lithosphere is solid and outer part of the Earth’s surface. This part includes the brittle upper portion of the mantle and the crust which is the outermost layers of Earth's structure. It is bounded by the atmosphere above and the asthenosphe below. It extends to a depth of about 60 mi (100 km). It is broken into about twelve separate, rigid blocks, or plates.
<h2>Answer to Q25</h2>
<u>The type of plate boundary where plates move apart, resulting in upwelling of material from the mantle to create is called </u><u>Divergent boundaries</u>
<h2>Explanation:</h2>
Divergent boundaries are present in the middle of the ocean. They contribute to seafloor spreading. When plates made of oceanic crust pull apart each other, a crack in the ocean floor appears from which the magma snoozes up from the mantle and fill in the space between the plates.
<h2>Answer to Q26.</h2>
<u>The correct option is </u><u>D. Electromagnetic radiation
</u>
<h2>Explanation:
</h2>
We know that there are many radioactive minerals present inside the earth. When these radioactive substance decay or produce radioactive radiation they melt the rocks in their surroundings. These rocks are then snoozed out by the area where the surface of the earth is comparatively soft. These areas are basically the volcanoes on the surface of earth. So we can say that the source of heat is electromagnetic radiations.
