Multiple choice

An oil drop spreads over water because

  1. Oil is lighter than water

  2. Oil is more viscous

  3. Oil does not mix with water

  4. Surface tension of oil is much smaller that of water

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Oil spreads on water because water's high surface tension creates a strong 'skin' effect. Oil has much lower surface tension, allowing it to form a thin film across the water surface. Density (option A) and viscosity (option B) are secondary factors.