When 3-bromo-2,4-dimethylpentane is treated with sodium hydroxide, only one alkene is formed?

3 bromo 2,4 dimethylpentane undergoes sn1 mechanism and hence forms a racemic mixture containing both r and s forms of the compound. in the first step that is the slow step a 2 degree carbocation is formed with positve charge at carbon 3 then it undergoes rearrangement to a 3 degree carbocation at carbon 2 from either side. as the carbocation contains 6 electrons in the outermost shell only it is sp2 hybridized and hence planar in structure, now the second step proceeds and the attack of -OH group takes place, as the -OH(hydroxyl) group can attack from either side, (top or bottom), hence a racemic mixture of 2,4 dimethyl pentan-2-ol is formed.

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.