Physical quantities are defined by magnitude and units

Steps:

• Define a physical quantity as something measurable in physics, like length or mass.
• Identify core attributes: every physical quantity has a numerical magnitude and associated units (e.g., meters for length).
• Distinguish from vectors: direction applies only to vector quantities, not all physical quantities.
• Evaluate choices: select the one capturing essentials without extras or omissions.

Why B is correct:

• Physical quantities are fundamentally scalars with magnitude (numerical value) and units for measurement, as per standard physics definitions (e.g., SI units system).

Why the others are wrong:

• A: Units are essential for quantification; omitting them makes it incomplete.
• C: Units are required to specify the scale; magnitude alone lacks context.
• D: Magnitude is the core numerical aspect; without it, no quantity exists.

Final answer: B