Distances in the solar system are often expressed in astronomical units to compare how far other objects are from the Sun relative to Earth’s orbit. One astronomical unit is the average distance from Earth to the Sun, which is about 149.6 million kilometers. Rounded for ease, that’s roughly 150 million kilometers. So the best answer is approximately 150,000,000 kilometers. The other numbers are far from the actual Earth–Sun distance: a few tens of thousands of kilometers is on the scale of Earth’s diameter or the Moon’s distance, and a distance around 1.5 billion kilometers would place you far beyond the outer planets.

Photosynthesis turns light energy into chemical energy stored in sugars, with oxygen released as a byproduct. In the chloroplasts, plants use light to drive reactions that combine carbon dioxide and water into glucose, a sugar, and release oxygen gas. That’s why the products are sugar (glucose) and oxygen. The other options describe inputs (water and carbon dioxide) or energy in a non-chemical form, or substances not produced by this process. Overall, the equation is: 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2.

Noble gases are a group of elements whose outer electron shells are full, giving them great stability and making them very unreactive. This full valence shell means they don’t easily gain, lose, or share electrons, so they don’t form compounds under normal conditions. They sit in Group 18 of the periodic table, and their atoms are typically monatomic gases at room temperature. The statement that best describes them is that they are a family of nonreactive nonmetals found in group 18 of the periodic table, which captures both their lack of reactivity and their position on the table. The other ideas aren’t right for this description: saying something about the outermost electrons alone doesn’t define noble gases, calling them an alloy would describe a mixture of metals, and claiming they form covalent bonds goes against their usual behavior of not bonding readily.

Elements are represented on the periodic table by short symbols, usually one or two letters, formed from their name. The first letter is always capitalized, and if there is a second letter it is lowercase. Helium’s symbol is He, derived from its name. That’s why helium is represented by He. For comparison, Hydrogen is H, Lithium is Li, and Beryllium is Be.