Question

The diagram below shows the first three periods of the modern periodic table. Three elements have been represented by the letters $X_1,X_2,$ and $X_3$. Arrange these elements in decreasing order of their atomic radii.

• A. $X_1>X_2>X_3$
• B. $X_3>X_1>X_2$
• C. $X_1>X_3>X_2$
• D. $X_2>X_1>X_3$

Answer 1

The correct option is B $X_3>X_1>X_2$

• Down the group, the atomic size increases. $X_3$ is below the other two elements, $X_2$ and $X_1$. So, the atomic size of $X_3$ is larger than $X_2$ and $X_1$
• Moving left to the right in a period, the atomic size decreases. $X_1$ comes before $X_2$, atomic size of $X_1>X_2$.
• So, the decreasing order is $X_3>X_1>X_2$​.
• Therefore, the correct answer is option B.