Athermistor is a device that can measure temperature with great accuracy. the principle is simple; the resistance of a semiconductor is measured and the temperature is then estimated based on knowledge of the temperature dependence of the resistivity of the semiconductor. consider a thermistor which is made of a pure (intrinsic) semiconductor. at 0°c a resistance of 10,000 sn is measured. at 100°c, the resistance is 420 q. if the resistance is 2000 q at tı, what is tı? [hint: assume constant electron and hole mobility over the above temperature range] (а) 15°c (b) 43°c** (c) 82°c (d) 66°c

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood. 

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.