Which of the following samples has the greatest density at STP?

• A. A block of magnesium (Mg)
• B. A block of aluminum (Al)
• C. A block of sodium (Na)
• D. A block of lead (Pb)

Answer: (D)

Verified step by step guidance

1. Recall that density (\(\rho\)) is defined as mass per unit volume: \(\rho = \frac{m}{V}\). To compare densities of different materials, we need to consider their intrinsic properties rather than just their physical state or size.
2. Understand that at STP (Standard Temperature and Pressure), the density of a solid block depends on the atomic mass and how closely the atoms are packed in the crystal structure. Therefore, the density is related to the molar mass and the volume occupied by one mole of the substance.
3. Look up or recall the approximate densities of the given metals: magnesium (Mg), aluminum (Al), sodium (Na), and lead (Pb). These values are typically found in tables or reference materials and reflect the mass per unit volume of each metal in solid form at STP.
4. Compare the densities of the metals. Lead (Pb) has a much higher atomic mass and a relatively compact atomic structure compared to magnesium, aluminum, and sodium, which results in a higher density.
5. Conclude that among the given options, the block of lead (Pb) has the greatest density at STP because it combines a high atomic mass with a dense atomic packing, leading to the greatest mass per unit volume.