Without any given values, predict which the following would possess the greatest density. So here we have the periodic table. And remember, the general trend is as we head up a group, our density decreases. There is no uniform trend when we're going across a period though, so we won't pay attention to that.
Now here we have lithium, we have barium, we have magnesium, beryllium and sodium. We can see that four of them are grouped closely together and then on the very bottom we have barium. Remember, the general trend is as we head up a group, our density decreases.
Since barium is the furthest down, we'd expect barium to have the greatest density out of the options that are given. That means that option B, barium would be our final answer.