Match column-$I$ with column-$II$ :

column-$I$	column-$II$
$a$. $Ra$	$p$. Aeroplane industry
$b$. $K$	$q$. Down cell
$c$. $Li$	$r$. Photo electric cell
$d$. $Na$	$s$. Radioactive

(A) $Ra$ (Radium) is a radioactive element $(a-s)$.
$K$ (Potassium) is used in photoelectric cells due to its low ionization energy $(b-r)$.
$Li$ (Lithium) is used in alloys for the aeroplane industry $(c-p)$.
$Na$ (Sodium) is extracted by the electrolysis of molten $NaCl$ in the Down cell $(d-q)$.
Therefore,the correct match is $a-s, b-r, c-p, d-q$.