Khalifa or Khalifah is a name or title which means "successor", "ruler" or "leader". It most commonly refers to the leader of a Caliphate, but is also used as a title among various Islamic religious groups and orders. Khalifa is sometimes also pronounced as "kalifa". There were 4 khalifas after Prophet Mohammed died, beginning with Abu Bakr. This was a difficult decision for the people to make, for no one except Prophet Mohammed had ever thought with foresight about who would rule after he would die. The Khilaafat (or Caliphate) was then contested and gave rise to the eventual division of the Islamic Umma into two groups, the Sunni and the Shi'a who interpret the word, Khalifa in differently nuanced ways.
<span>No2 would be the free radical as it has an unpaired electron in it's grouping. Since free radicals are defined by the attribute of having an unpaired electron in their make-up, no2 fits this definition.</span>
Answer:Sumerian farmers' invention of the plow helped them provide their city-states with a stable food supply. Before farmers invented the plow, they used animal horns or pointed sticks to poke holes in the earth.
