What is Huckel's rule

In numbering carbon atoms in the parent chain of a hydrocarbon, why would you number from right to left, rather than left to right

Ammonium perchlorate nh4clo4 is the solid rocket fuel used by the u. s. space shuttle. it reacts with itself to produce nitrogen gas n2 , chlorine gas cl2 , oxygen gas o2 , water h2o , and a great deal of energy. what mass of nitrogen gas is produced by the reaction of 2.1g of ammonium perchlorate?

The diagram shows the relationship between scientific disciplines. the names of some scientific disciplines have been removed from the boxes. which scientific discipline belongs in the blue box? a. physics b. biology c. chemistry d. metallurgy