**Explanation:**

In the periodic table, elements are arranged in periods and groups. A period refers to a horizontal row, while a group refers to a vertical column. Each period represents the energy level or shell that electrons occupy around the nucleus of an atom.

**a) Across a period electropositivity of elements increases:**
This statement is incorrect. Electropositivity refers to the tendency of an element to lose electrons and form positive ions. As we move across a period from left to right, the electronegativity of elements generally increases, which means they have a greater tendency to attract electrons rather than lose them. Therefore, the electropositivity of elements decreases across a period.

**b) Across a period basic nature of oxides increases:**
This statement is incorrect. Basic nature refers to the ability of an oxide to react with water and produce a basic solution. As we move across a period from left to right, the basic nature of oxides generally decreases. Elements on the left side of the periodic table, such as metals, tend to form basic oxides, while elements on the right side, such as non-metals, tend to form acidic or neutral oxides. Therefore, the basic nature of oxides decreases across a period.

**c) Across a period acidic nature of oxides increases:**
This statement is correct. Acidic nature refers to the ability of an oxide to react with water and produce an acidic solution. As we move across a period from left to right, the acidic nature of oxides generally increases. Elements on the right side of the periodic table, such as non-metals, tend to form acidic or neutral oxides. These oxides react with water to produce acidic solutions. Therefore, the acidic nature of oxides increases across a period.

**d) Across a period metallic character increases:**
This statement is incorrect. Metallic character refers to the ability of an element to exhibit metallic properties, such as conductivity and malleability. As we move across a period from left to right, the metallic character generally decreases. Elements on the left side of the periodic table, such as metals, exhibit strong metallic character. However, as we move towards the right side, the elements become less metallic and more non-metallic in character. Therefore, the metallic character decreases across a period.

Because non metallic character increased and non metals formed acidic oxides.