4/10 What percentage of the total atomic mass of magnesium bromide (MgBr_(2)) is composed of magnesium? 87% 63% 13% 43%

To determine the percentage of the total atomic mass of magnesium bromide (MgBr₂) that is composed of magnesium, we need to follow these steps:<br /><br />1. **Find the atomic masses of magnesium (Mg) and bromine (Br).**<br /> - The atomic mass of magnesium (Mg) is approximately 24.305 u.<br /> - The atomic mass of bromine (Br) is approximately 79.904 u.<br /><br />2. **Calculate the molar mass of magnesium bromide (MgBr₂).**<br /> - Magnesium bromide consists of one magnesium atom and two bromine atoms.<br /> - Molar mass of MgBr₂ = (1 × atomic mass of Mg) + (2 × atomic mass of Br)<br /> - Molar mass of MgBr₂ = (1 × 24.305 u) + (2 × 79.904 u)<br /> - Molar mass of MgBr₂ = 24.305 u + 159.808 u<br /> - Molar mass of MgBr₂ = 184.113 u<br /><br />3. **Calculate the percentage of the total atomic mass of MgBr₂ that is composed of magnesium.**<br /> - Percentage of magnesium = (atomic mass of Mg / molar mass of MgBr₂) × 100%<br /> - Percentage of magnesium = (24.305 u / 184.113 u) × 100%<br /> - Percentage of magnesium ≈ 0.132 × 100%<br /> - Percentage of magnesium ≈ 13.2%<br /><br />Therefore, the percentage of the total atomic mass of magnesium bromide (MgBr₂) that is composed of magnesium is approximately 13%.<br /><br />So, the correct answer is:<br />$13\%$