Final answer:
The atomic number of element Y is 5, corresponding to the element Boron on the periodic table, which is two places to the right of element X (Lithium) with an atomic number of 3.
Step-by-step explanation:
Since element X has an atomic number of 3, which corresponds to Lithium on the periodic table, we need to determine the atomic number of element Y based on its position relative to element X. The periodic table is arranged so that elements are in order of increasing atomic number from left to right, and each row corresponds to a period. Considering this arrangement, if element X (with atomic number 3) is two places left of element Y, then element Y would logically have an atomic number two units higher, making the atomic number of Y equal to 5.
Therefore, the correct answer is A. 5, which is the atomic number of the element Boron.