The density of a certain oil on frying becomes 0.4 kgm ^ -3 with the volume of 20m ^ 3 . what will be its…

Analyze the question: The oil's mass stays the same, because no oil is lost to spillage. Only the density and volume change. We are given the final state (after frying) and asked for the initial volume.

Concept: Mass = density × volume, so if the mass is constant:

ρ₁V₁ = ρ₂V₂

Solution:

• Initial density, ρ₁ = 0.8 kg/m³, initial volume V₁ = ?
• Final density, ρ₂ = 0.4 kg/m³, final volume V₂ = 20 m³

Mass after frying = 0.4 × 20 = 8 kg

Since the mass is unchanged:

0.8 × V₁ = 8

V₁ = 8 ÷ 0.8 = 10 m³

Check: 0.8 × 10 = 8 kg, which equals 0.4 × 20 = 8 kg. ✓

(Notice that the density halves, so the volume doubles. Working backwards from 20 m³ gives 10 m³.)

Answer: Option B, 10 m³.

Exam tip: Whenever a question says "no loss" or "no spillage," think "mass is constant" and use ρ₁V₁ = ρ₂V₂. Density and volume are inversely proportional when the mass stays the same.