Final answer:
Considering the periodic trends, the atoms Sr, Rb, Mg, and Na are arranged in order of increasing atomic size as Mg < Na < Sr < Rb.
Step-by-step explanation:
The question asks to arrange the atoms Sr, Rb, Mg, and Na in order of increasing atomic size. To correctly arrange them, we need to understand the trend in atomic radii on the periodic table. Atomic radii increase as we move down a group and decrease as we move from left to right across a period. Keeping this in mind and looking at the periodic table, we can conclude the order of atoms from smallest to largest is: Mg < Na < Sr < Rb. Magnesium (Mg) is small because it is to the right of sodium (Na) in the same period. Sodium is smaller than strontium (Sr) because Sr is located further down the same group. Lastly, rubidium (Rb), which is in the same group but one period below Sr, is the largest among them.