*Question*
Q: In contrast to metals, electrical insulators are materials that conduct electricity poorly because their valence bands are what? Read this paragraph and choose the correct option from the provided answers: Insulators In contrast to metals, electrical insulators are materials that conduct electricity poorly because their valence bands are full. The energy gap between the highest filled levels and the lowest empty levels is so large that the empty levels are inaccessible: thermal energy cannot excite an electron from a filled level to an empty one. The valence-band structure of diamond, for example, is shown in part (a) in . Because diamond has only 4 bonded neighbors rather than the 6 to 12 typical of metals, the carbon 2s and 2p orbitals combine to form two bands in the solid, with the one at lower energy representing bonding molecular orbitals and the one at higher energy representing antibonding molecular orbitals. Each band can accommodate four electrons per atom, so only the lower band is occupied. Because the energy gap between the filled band and the empty band is very large (530 kJ/mol), at normal temperatures thermal energy cannot excite electrons from the filled level into the empty band. Thus there is no pathway by which electrons can move through the solid, so diamond has one of the lowest electrical conductivities known. Figure 12.23 Energy-Band Diagrams for Diamond, Silicon, and Germanium. Choices: - empty - large - half-full - full A:
**Answer**
full

*Question*
Q: What is a process in which some substances change into different substances? Read this paragraph and choose the correct option from the provided answers: A chemical reaction is a process in which some substances change into different substances. In a chemical reaction, bonds break in reactants and new bonds form in products. Choices: - a toxic reaction - a bio reaction - a thermodynamic reaction - a chemical reaction A:
**Answer**
a chemical reaction

*Question*
Q: What does burning wood release into the atmosphere? Read this paragraph and choose the correct option from the provided answers: Forests are also being destroyed. Trees may be cut down for their wood, or they may be burned to clear the land for farming. Burning wood releases more carbon dioxide into the atmosphere. You can see how a tropical rainforest was cleared for farming in Figure below . With forests shrinking, there are fewer trees to remove carbon dioxide from the air. This makes the greenhouse effect even worse. Choices: - oxygen - helium - hydrogen chloride - carbon dioxide A:
**Answer**
carbon dioxide

*Question*
Q: What is used during filtration to push fluids and solutes, from higher pressure areas to lower pressure areas? Read this paragraph and choose the correct option from the provided answers: Another mechanism besides diffusion to passively transport materials between compartments is filtration. Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluidand the solutes within itfrom a higher pressure area to a lower pressure area. Filtration is an extremely important process in the body. For example, the circulatory system uses filtration to move plasma and substances across the. Choices: - constructs pressure gradient - limited pressure gradient - magnesium pressure gradient - hydrostatic pressure gradient A:
**Answer**
hydrostatic pressure gradient