Atomic Models

Max Planck is known for his contributions to quantum theory, especially for the development of Planck's constant and the concept of quantized energy, but he did not propose an atomic model. The atomic models were proposed by:

Bohr: The Bohr model proposed that electrons move in orbits around the nucleus, with quantized energy levels.
Sommerfeld: He extended the Bohr model by introducing elliptical orbits and explaining fine structure.
Schrodinger: He formulated the wave mechanics model of the atom, which describes the behavior of electrons as matter waves.

Thus, Planck did not propose an atomic model.

The correct option is (A): Planck

To solve the problem of identifying elements with 5, 6, or 7 valency electrons, it's crucial to understand the concept of valency and electron configuration.

The valency of an element refers to its ability to bond with other atoms, determined by its outermost electrons (valence electrons). Elements with 5, 6, or 7 valency electrons are typically nonmetals found in Groups 15-17 of the periodic table.

Let's examine the elements given in the options:

• P (Phosphorus): Located in Group 15, has 5 valence electrons.
• S (Sulfur): Located in Group 16, has 6 valence electrons.
• Cl (Chlorine): Located in Group 17, has 7 valence electrons.
• Na (Sodium): Located in Group 1, has 1 valence electron, making it unsuitable for this query.

By evaluating the provided options:

• P, S, Cl → Correct. Each element falls within the 5-7 valency electron range.
• P, Cl, Na → Incorrect. Na has only 1 valence electron.
• P, Cl, S → Correct. Reordering doesn't change correctness, but matches first option anyway.
• P, S, Na → Incorrect. Na is not in the 5-7 valency electron range.

Thus, the correct answer is P, S, Cl, as all these elements have the required number of valency electrons.