Consider the following statements: Which of these statements are correct?

Answer: (a) 1, 2 and 3

Mixed state, main gases and hotter basalt are right; the horizontal sheet is a sill.

Statement by statement

1. ✓ CORRECT Magma is molten rock with crystals and gases.

2. ✓ CORRECT Water vapour and CO₂ are its main dissolved gases.

3. ✓ CORRECT Basaltic magma (~1,100–1,200 °C) is hotter than silicic magma.

4. ✗ WRONG A horizontal sheet between layers is a SILL; a dyke cuts across layers vertically.

The idea

Magma is a mixture whose behaviour depends on temperature, silica content, crystals and dissolved gases. As it cools below ground, it forms an intrusion. Intrusions are named partly by whether they follow existing rock layers or cut across them.

Magma contains melt, crystals and dissolved gas → Magma enters a crack underground → It follows a layer or cuts across layers → Heat escapes into surrounding rock → Crystals grow → An intrusive rock body remains

Why the others are wrong

(b) Accepts the dyke.

(c) Accepts the dyke.

(d) Accepts the dyke.

The trap

Sill vs dyke — horizontal vs vertical.

Elimination technique

Statement 4 names a layer-parallel intrusion as a dyke. That is a sill, so every option containing 4 falls; only (a) remains.

Also know

A sill follows existing layers; a dyke cuts across them, so orientation relative to bedding matters more than simply horizontal versus vertical. A laccolith arches the overlying layers, while a batholith is a large intrusive body. Silica-rich magma is generally more viscous than basaltic magma; gases escape less easily from a viscous melt.