Questions

When atoms react they do so in order to reach the lowest energy, which is the most stable. The electrons orbitals will overlap in the way that reduces the energy the most. Orbitals of similar energy will produce the greatest stabilisation.The answer you gave isn't the whole story, it depends what species is reacting with what. The effective nuclear charge on the atom will affect the energy of the valance electrons.

Hence, the reactivity of an atom arises from the existence of unpaired electrons in the valence shell.

5 Mhz is the Maximum clock frequency in 8086.

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Iteration means doing something again and again, repeatedly,... 

Hence, looping is a process of repeating a method and so it is similar in meaning to Iteration.