Because the number of valence electrons of an element determines the properties and in particular the reactivity of that element.
In fact, elements of the first group (i.e. only one valence electron) have high reactivity, because they can easily give away their valence electron to atoms of other elements forming bonds. On the contrary, elements of the 8th group (noble gases) have their outermost shell completely filled with electrons, so they do not have valence electrons, and they have little or no reactivity at all.
Yes, <span> the moon fall partly into earth's shadow when it is in its full size</span>
Explanation:
It is given that,
Frequency of monochromatic light,
Separation between slits,
(a) The condition for maxima is given by :
For third maxima,
(b) For second dark fringe, n = 2
Hence, this is the required solution.