My five year old step son does not behave properly with me and answers me back. My wife does not like me scolding her. What do I do?

This must be because he thinks you to be a villain in his life, as you are the person with whom he has to share his mother's love. Plus, he hasn't seen you during all these years and you are a new person living with them and who takes the attention of his mother. I think you need to develop a bond with him. You first of all need to show him that you are taking his mother away from him and that his mother still loves him the most. Make sure you do not expressive about your love for his mother in front of him. Give him time to accept you. You can make him like you by planning to do activities with him. As a family go for a holiday, picnics, outings, fishing, skiing etc. Do these activities more often, it will develop your bonding with him. http://www.helpguide.org/articles/family-divorce/step-parenting-blended-families.htm