**Acknowledgements**

I am grateful to Almighty Allah, lord of the universe and source of wisdom and guidance, who enable us to complete this chapter. With all respect to his Holy Prophet Muhammad (PBUM) who brought the light of knowledge when humanity was wandering in the desert of ignorance.

I am grateful to Dr. Samina Ashraf for her attitude; suggestions, sincere authorship, guidance and kind help during this chapter. I am humbly thankful to my dearest parents and family members who are very generously provided me with every facility at every stage of my life and make it possible for me to complete this chapter.

I am also very grateful to Sara Debeuc for her true professional attitude and for providing me with such a wonderful opportunity and bearing my numerous questions.
