Explanation:

When we are given the formula of a compound, X3Y, we can determine the valencies of elements X and Y by analyzing the subscript numbers.

The subscript number after element X is 3, which indicates that there are three atoms of element X present in the compound. Similarly, the subscript number after element Y is 1, which indicates that there is only one atom of element Y present in the compound.

From this information, we can determine the valencies of elements X and Y.

Valency of element X:
The valency of an element is defined as the combining capacity of an element with other elements. In this case, since there are three atoms of element X present in the compound, we can determine the valency of X as follows:

Valency of X = Total number of electrons in the outermost shell of X - Number of electrons required to complete its octet

To determine the total number of electrons in the outermost shell of X, we need to know the electronic configuration of X. Since the question does not provide this information, we cannot determine the exact valency of X. However, based on the given options, option A (1 and 3) is the most likely answer.

Valency of element Y:
Since there is only one atom of element Y present in the compound, we can determine the valency of Y as follows:

Valency of Y = Total number of electrons in the outermost shell of Y - Number of electrons required to complete its octet

Similar to element X, we need to know the electronic configuration of Y to determine its valency accurately. However, based on the given options, option A (1 and 3) is the most likely answer.

Therefore, based on the given formula X3Y, the valencies of elements X and Y are most likely 1 and 3, respectively.