Is SL arora really important(or the best book) for physics in 12th for cbse boards? Is there any alternative. Its very time consuming. If its important then what chapters shud i totally do from sl arora?

There is nothing far better book than only and only

evergreen boo that is

"NCERT PHYSICS” for cbse students.

First u must know your ncert book.

Read well

practice well from it and proceed to other guide books such as SL Arora.

U can also refer "Pradeep". 

@ tanisha 
Yes , its a time consuming book , but the main thing that u will get from this book is this book follow a proper shortcut path for derivation and it will make your concept crystall clear for the upcoming entrance exam like jee and pmt . 
and yes , alternatives are there if u want that for boards only . 
TAKE ARIHANT ALL IN ONE , 
THATS the complete book itself for board exam . and by following that it also have a good approach to derivation as well as its questions are usefull also . 
and always remember – not to ignore ncert , and follow all in one simoultaneously . 
and also do previous year question paper bank from arihant . they are at most required to have a good grasp over numericals . 
ALL THE BEST ..