Fill in the following blanks with suitable words: (a) The form of carbon which is known as black lead is . (b) The form of carbon which is used as a lubricant at high temperature is . (c) Compounds of carbon with hydrogen alone are called . (d) CnH2n is the general formula of hydrocarbons. (e) Hydrocarbons having the general formula CnH2n-2 are called . (f) Ethene and ethyne are examples of hydrocarbons. (g) Ethyne has carbon-hydrogen single bonds. (h) Carbon compounds have usually melting points and boiling points because they are in nature. (i) The property of carbon atoms to form long chains in compounds is called . (j) The general formula CnH2n for cycloalkanes is the same as that of . (k) The IUPAC name of ethylene is . (l) The IUPAC name of acetylene is .