To determine which atom fits the given properties, we need to analyze each of the criteria provided: 1. **Relative atomic mass greater than 30 but less than 40**: This means we are looking for elements with atomic masses in the range of 31 to 39. 2. **Odd atomic number**: The atomic number of the element must be an odd number. Atomic numbers correspond to the number of protons in the nucleus of an atom. 3. **Forms a unipositive ion in solution**: A unipositive ion means that the atom can lose one electron to form a cation with a +1 charge. This is common for metals, particularly those in groups 1 and 2 of the periodic table, as well as some transition metals. ### Step-by-Step Analysis 1. **Identify Elements with Atomic Masses Between 30 and 40**: - The elements that fall within this range include: - Gallium (Ga) - Atomic mass ~ 69.72 (not in range) - Germanium (Ge) - Atomic mass ~ 72.63 (not in range) - Arsenic (As) - Atomic mass ~ 74.92 (not in range) - Scandium (Sc) - Atomic mass ~ 44.96 (not in range) - Titanium (Ti) - Atomic mass ~ 47.87 (not in range) - Vanadium (V) - Atomic mass ~ 50.94 (not in range) - Chromium (Cr) - Atomic mass ~ 51.96 (not in range) - Manganese (Mn) - Atomic mass ~ 54.94 (not in range) - Iron (Fe) - Atomic mass ~ 55.85 (not in range) - Cobalt (Co) - Atomic mass ~ 58.93 (not in range) - Nickel (Ni) - Atomic mass ~ 58.69 (not in range) - Copper (Cu) - Atomic mass ~ 63.55 (not in range) - Zinc (Zn) - Atomic mass ~ 65.38 (not in range) - Gallium (Ga) - Atomic mass ~ 69.72 (not in range) - Arsenic (As) - Atomic mass ~ 74.92 (not in range) - Selenium (Se) - Atomic mass ~ 78.96 (not in range) - Bromine (Br) - Atomic mass ~ 79.90 (not in range) - Krypton (Kr) - Atomic mass ~ 83.80 (not in range) However, if we consider the elements in the range of 30-40, we find: - **Copper (Cu)** - Atomic number 29 (not odd) - **Zinc (Zn)** - Atomic number 30 (not odd) - **Gallium (Ga)** - Atomic number 31 (odd) - **Germanium (Ge)** - Atomic number 32 (not odd) - **Arsenic (As)** - Atomic number 33 (odd) - **Selenium (Se)** - Atomic number 34 (not odd) - **Bromine (Br)** - Atomic number 35 (odd) - **Krypton (Kr)** - Atomic number 36 (not odd) - **Rubidium (Rb)** - Atomic number 37 (odd) - **Strontium (Sr)** - Atomic number 38 (not odd) - **Yttrium (Y)** - Atomic number 39 (odd) 2. **Check for Unipositive Ion Formation**: - **Gallium (Ga)**: Can form Ga³⁺, but not Ga⁺. - **Arsenic (As)**: Can form As³⁺, but not As⁺. - **Bromine (Br)**: Can form Br⁻, but not Br⁺. - **Rubidium (Rb)**: Forms Rb⁺ (unipositive ion). - **Yttrium (Y)**: Forms Y³⁺, but not Y⁺. ### Conclusion From the analysis, the only element that meets all three criteria is **Rubidium (Rb)**, which has an atomic mass of approximately 85.47, an odd atomic number of 37, and forms a unipositive ion (Rb⁺) in solution. ### Summary of Options: - **A. T**: Not applicable as it does not meet the criteria. - **B. W**: Not applicable as it does not meet the criteria. - **C. X**: Not applicable as it does not meet the criteria. - **D. Y (Rubidium)**: Correct answer as it meets all criteria. ### Revision Summary: - Identify elements based on atomic mass and atomic number. - Check for the ability to form unipositive ions. - Ensure all criteria are met before selecting an answer. - Remember that odd atomic numbers and specific ion formation are key to solving such problems.