A.RATE B.EXTENT C.LEVEL D.POINTTASK 2

80. A.rate B.extent C.level D.pointTask 2: READING COMPREHENSIONRead the passage and choose the best answer for each question below.The ability to conduct electricity is one of the key properties of a metal. Othersolid material such as silicon can conduct electricity but only effectively at certaintemperatures. Also, some substances such as salt (sodium chloride) can conduct whenmolten or when dissolved in water. The ability of metals to conduct electricity is due tohow their atoms bond together. In order to bond together the metal atoms lose at least oneof their outermostelectrons. This leaves the metal atoms with a positive charge and theyare now strictly ions. The lost electrons are free to move in what are known as a sea ofelectrons. Since the electrons are negatively charged they attract the ions and this is whatkeeps the structure together.An electric current is a flow of charge and since the electrons in the sea ofelectrons are free to move they can be made to flow in one direction when a source ofelectrical energy such as a battery is connected to the metal. Hence we have an electriccurrent flowing through the wire, and this is what makes metals such good conductors ofelectricity. The only other common solid conducting material that pencil users are likelyto encounter is graphite (what the ‘lead’ of a pencil is made from). Graphite is a form ofcarbon and again the carbon atoms bond in such a way that there is a sea of electrons thatcan be made to flow as an electric current. Likewise, if we have an ionic substance likesalt we can make the electrically charged ions flow to create a current but only whenthose ions are free to move, either when the substance is a liquid or dissolved in water. Inits solid state an ionic substance like salt cannot conduct electricity as its charged ionscannot flow.Electrical insulators are substances that cannot conduct electricity well either,because they contain no charged particles or any charged particles theymight contain donot flow easily. Water itself is a poor conductor or electricity as it does not contain asignificant amount of fully charged particles (the ends of a water molecule are partlycharged but overall the molecule is neutral). However, most water we encounter doescontain dissolved charged particles, so it will be more conductive than pure water. Manyof the problems that occur when touching electrical devices with wet hands result fromthe ever-present salt that is left on our skin through perspiration and it dissolves in thewater to make it more conductive.