What is the function of iodic acid in the iodination of alkanes? Can we use any other substance in its place?

What is alternation effect?

Define cracking. 

During the pyrolysis of alkanes C-C bonds break in preference to C-H bond. Why?

Arrange the following compounds in order of their increasing boiling points:
n-Pentane, n-Hexane, Ethane, 2-2-Dimethylpentane, 2-Methylpentane.