Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
$F, Na, Mg, Al, Si, P, S, Cl, Ar, K$
$(a)$ Pick two sets of elements which have similar properties.
$(b)$ The given sequence represents which law of classification of elements?

(A) The two sets of elements with similar properties are:
$(i)$ $F$ and $Cl$ (both are halogens).
$(ii)$ $Na$ and $K$ (both are alkali metals).
$(b)$ The given sequence represents Newland's Law of Octaves,which states that when elements are arranged in increasing order of their atomic masses,the properties of every eighth element are a repetition of the properties of the first element.