Explanation:

The Periodic Table:
The periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties. It is divided into periods (horizontal rows) and groups (vertical columns). The elements in the periodic table can be broadly classified into metals, non-metals, and metalloids.

Non-metals:
Non-metals are a group of elements in the periodic table that generally have low melting and boiling points, poor electrical and thermal conductivity, and tend to gain electrons in chemical reactions. Examples of non-metals include hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, and halogens such as fluorine, chlorine, and iodine.

Higher Atomic Number:
The atomic number of an element corresponds to the number of protons in the nucleus of its atom. In the periodic table, elements are arranged in order of increasing atomic number. As we move across a period from left to right, the atomic number increases. Therefore, in the same period, non-metals have a higher atomic number compared to metals.

Explanation of the Options:
a) Atomic number: As mentioned above, non-metals have a higher atomic number compared to metals in the same period.
b) Atomic size: Atomic size generally decreases across a period due to increased effective nuclear charge. This means that non-metals in the same period have smaller atomic sizes compared to metals.
c) Electropositivity: Electropositivity refers to the tendency of an atom to lose electrons and form positive ions. Non-metals tend to be electronegative, meaning they have a strong tendency to gain electrons rather than lose them. Therefore, non-metals have lower electropositivity compared to metals.
d) All of the mentioned: This option is incorrect because non-metals do not have higher atomic size or electropositivity compared to metals in the same period. Only the atomic number is higher for non-metals in the same period.

In Summary:
Non-metals have higher atomic number compared to metals in the same period, but they do not have higher atomic size or electropositivity. The correct answer is option 'a' – Atomic number.