B.
When the object has passed over the observer, the pressure disturbance waves (Mach waves) radiate toward the ground, causing a sonic boom. ... Then, just as the aircraft bursts through the sound barrier, the air is locally disturbed by the resulting shock wave and the condensation/vapor cloud disappears.
Answer: Matter is heated, and its particles spread out more
Explanation:
Thermal expansion occurs when there's an expansion of an object or material or when an object becomes bigger because of a rise in its temperature. This brings about the faster movement of the heated molecules and the atoms spreading out.
Therefore, the cause and effect of thermal expansion will be that when matter is heated, and its particles spread out more.
Answer:
Option D is correct. MgO has a higher melting point because the ions have larger charges.
Explanation:
Magnesium oxide contains higher melting point compare to sodium chloride, because of its Mg2+, and O2- ions contain greater number of charges, and helping to form strong ionic bonds compare to Na+, and Cl- ions in Nacl.
That's why melting point of magnesium oxide is more than sodium chloride. MgO molecules bounded with each other with very high force known as electrostatic attraction present between negatively charge oxygen, and positively charge magnesium ions.