To determine which of the elements R, T, W, X, or Y is an alkali metal based on the compounds they form, we need to analyze the properties of the compounds mentioned and the characteristics of alkali metals. ### Step-by-Step Explanation 1. **Understanding Alkali Metals**: - Alkali metals are found in Group 1 of the periodic table. They include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). - These metals are characterized by their tendency to form basic oxides and hydrides. They react vigorously with water to produce hydroxides and hydrogen gas. 2. **Analyzing the Compounds**: - **Basic Hydride (R.H)**: This indicates that R is likely a metal that can form a hydride with a basic character. Alkali metals typically form basic hydrides. - **Acidic Hydride (YH)**: This suggests that Y is likely a non-metal or a metalloid that can form an acidic hydride. Non-metals like hydrogen (H), carbon (C), and nitrogen (N) can form acidic hydrides. - **Atmospheric Oxide (W₂O₃)**: This oxide suggests that W is likely a metal that can form a trivalent oxide. This is not typical for alkali metals, which usually form oxides with a +1 oxidation state (e.g., Na₂O). - **XO₂**: This indicates that X is likely a non-metal or a metalloid that can form a dioxide. Non-metals like carbon (C) and silicon (Si) can form dioxides. 3. **Identifying the Alkali Metal**: - Given that R forms a basic hydride (R.H), it is reasonable to conclude that R is an alkali metal. The basic nature of the hydride aligns with the properties of alkali metals. - The other compounds do not suggest that T, W, or X are alkali metals based on their respective characteristics. ### Why Other Options Are Incorrect - **Option B (T)**: There is no information provided that suggests T forms a basic hydride or any characteristic that aligns with alkali metals. Therefore, T is not an alkali metal. - **Option C (W)**: W forms an oxide (W₂O₃) that suggests it is a metal that can exhibit a +3 oxidation state. This is not characteristic of alkali metals, which typically form +1 oxidation states in their oxides. - **Option D (X)**: X forms a dioxide (XO₂), which is characteristic of non-metals or metalloids, not alkali metals. Alkali metals do not form dioxides. ### Summary of Key Points - **Alkali Metals**: Group 1 elements that form basic hydrides and oxides. - **Basic Hydride (R.H)**: Indicates R is likely an alkali metal. - **Acidic Hydride (YH)**: Suggests Y is a non-metal. - **W₂O₃ and XO₂**: Indicate that W and X are not alkali metals. ### Revision Summary - Alkali metals are found in Group 1 and form basic hydrides and oxides. - R is identified as the alkali metal due to the formation of a basic hydride. - W and X do not exhibit properties characteristic of alkali metals. - Understanding the nature of the compounds formed helps in identifying the type of elements involved. Thus, the correct answer is **A. R**.