Riding high under the leadership of Satya Nadella, Microsoft has surpassed Exxon Mobil to become the second-most valuable company in the world, placing it just behind Apple, which holds the top spot. The companies swapped places last week when concerns about the falling price of oil brought Exxon’s shares down. The energy giant’s market capitalization fell to $401.9 billion on Friday from $403.9 billion on Wednesday.