Group 1 elements are alkali metals, Group 2 are alkaline earth metals, and Group 17 are halogens. Only statement 3 is correct as written in the options provided.

Newlands' Law of Octaves had several limitations, one of which was the grouping of dissimilar elements together and the separation of similar elements. Specifically, iron (Fe) was placed in the same column as oxygen and sulfur, despite its chemical properties being much more similar to cobalt (Co) and nickel (Ni), which were placed in a different group.

Dobereiner's triads were groups of three elements with similar properties where the atomic weight of the middle element was approximately the average of the other two. In the triad of phosphorus (atomic weight ~31), arsenic (~75), and antimony (~122), arsenic acts as the middle element, as (31+122)/2 is approximately 76.5, which is close to the atomic weight of arsenic.

Every chemical element is assigned a unique chemical symbol, typically consisting of one or two letters derived from its English or Latin name (e.g., H for Hydrogen, Fe for Iron). These symbols provide a standardized international shorthand for representing elements in chemical formulas and equations.

Period 2 contains several non-metals including carbon, nitrogen, oxygen, and fluorine. While other periods also contain non-metals, Period 2 is characterized by a high concentration of these elements relative to the total number of elements in that period, making it a significant region for non-metallic chemistry.

The modern periodic table is organized based on the atomic number, which dictates the electronic configuration of an atom. Since the valence shell electronic configuration determines how an atom interacts with others, it directly influences both physical properties (like atomic radius and melting point) and chemical properties (like reactivity and valency). Thus, periodic trends in both categories are explained by electronic structure.

Lothar Meyer plotted physical properties such as atomic volume against atomic weight. He observed a periodic pattern, leading him to conclude that the properties of elements are a periodic function of their atomic weights. While modern chemistry uses atomic number, Meyer's work was foundational in establishing the concept of periodicity based on the data available during his time.

Lanthanum is a chemical element with the symbol La and atomic number 57. It is the first element of the lanthanide series, which follows barium (atomic number 56) in the periodic table, marking the beginning of the f-block filling in the sixth period.

Henry Moseley (often spelled Mozley in older texts) established the modern periodic law through his X-ray spectroscopy experiments. He demonstrated that the frequency of X-rays emitted by elements is proportional to the square of their atomic number, rather than their atomic mass, thereby correcting the basis for periodic classification.

In the fourth period, Germanium and Arsenic are metalloids. In the fifth period, Antimony and Tellurium are metalloids. Thus, periods 4 and 5 each contain two metalloids.