Answer
According to the “logical” sequence of quantum numbers, europium element would be chemically similar to sodium.
Work Step by Step
The number of electrons in per shell (having principle quantum number $n$) is calculated by the formula: $ N=2n^2$
An atom of europium has $63$ electrons. According to the “logical” sequence of quantum numbers, the shells will be occupied by $2, 8,18, 32$ respectively in first $4$ shells. So total $60$ electrons will be occupied in first $4$ shells. Among remaining $3$ electrons, $2$ will go to $5s$ state and last one will go into $5p$ state. Sodium has $11$ electron. According to the “logical” sequence of quantum numbers, the shells will be occupied by $2, 8$ respectively in first $2$ shells. Remaining $1$ electron will go to $3s$ state. Thus in both cases, there is only one electron in outermost sate. Thus, according to the “logical” sequence of quantum numbers, europium element would be chemically similar to sodium.