Question

_________ 1. an allotrope of carbon that is soft and can be used as a lubricant is ______.

Answer 1

1. An allotrope of carbon that is soft and can be used as a lubricant is d. graphite.
Graphite is the most stable allotrope of carbon under standard conditions (pressure and temperature). In graphite carbon atoms have sp2 hybridization, because of that graphite has ability to conduct electricity and heat.

2. The process by which a solid changes directly to a gas without first becoming a liquid is called c. sublimation.
Sublimation is an endothermic process. For example dry ice (carbon(IV) oxide in solid state) is used because of sublimation in nightclubs, fog machines, at theaters, haunted house attractions.

3. In the gaseous state d. halogens form diatomic covalent molecules.
Halogen diatomic molecules (17 group in the periodic table, halogen means "salt producing) in the gaseous state in room temperature are fluorine (F₂) and chlorine (Cl₂). Both molecules have single covalent bond and they are very reactive.

4. When hydrogen reacts with the active metals, it b. gains one electron.
Active metals are I group of Periodic table of elements (alkaline metals). Alkaline metals are lithium, sodium, rubidium, potassium, cesium. They have low ionization energy and lose one electron very easy. Compounds with hydrogen with this metals are called hydrides.

5. Different forms of the same element that have different properties because of different atom arrangements are called a. allotropes.
Carbon has many allotropes, but two most important are graphite and diamomd. Graphite has sp2 and diamond has sp3 hybridization of carbon atoms, because of that graphite conduct electricity and diamond not.

6. At room temperature, most metals are b. solids.
Most metals have strong metallic bond, because strong electrostatic attractive force between valence electrons (metals usually have low ionization energy and lose electrons easy) and positively charged metal ions.
They also form crystal lattice and because of that has high melting points.

7. An allotrope of carbon that is hard and is often used in jewelry is b. diamond.
In diamond carbon atoms are arranged in the face centered cubic crystal structure called a diamond lattice.
Diamond has very strong covalent bonds between carbon atoms and because of that it has the highest hardness and thermal conductivity of any bulk substance. 

8. Metals can be used as wire because they are a. ductile.
Ductility is a measure of a material's (in this example metal) ability to undergo deformation before rupture. For example gold is very ductile and can be drawn into a monoatomic wire.
Malleability is a material's ability to deform under compressive stress.

9. The d. transition elements often occur in nature as uncombined elements.
Uncombined elements are in elemental form and do not attache with other elements. Several transition elements (metals) like gold, silver, rhodium, palladium and platinum are unreactive and are resistant to oxidation and corrosion.