:NOTE::::In the question eq mass of element is mentioned
We know
Molecular weight=2 * vapor density
Eq wt*valency=2*vap density
Now eq wt will be....eq wt of element+chlorine=24+35.5=59.5
Therefore,
59.5*valency=2*59.5
Val=2
Asked is atomic mass of elemen and eq wt of element is given we have done all the above for finding valency.
Eq wt*Val=at wt
24*2 which comes to 48