For solving the questions of  finding  modulus and argument if we don't do it in the way it is given in topper ncert solutions then will the answer be wrong or will i get less marks?

There are multiple methods in finding modulus and argument of a complex number. 

Topper has followed the standard methods which are given in the reference text book for a specific class. 

So it is advised to follow the same method but its not compulsary. You can use even other methods as well and you will be given marks accordingly provided your solution is correct.