Statement I: Decay and disintegration of rocks in situ is called weathering Statement II: Mechanical weathering is mainly caused by temperature variation

Statement I is true as weathering is defined as the mechanical disintegration and chemical decomposition of rocks through the action of weather elements [2]. It is characterized as an in-situ or on-site process because it involves little to no motion of materials, distinguishing it from erosion [2]. Statement II is also true; mechanical (physical) weathering involves the disintegration of rocks due to molecular stresses induced by temperature changes, thermal expansion, and contraction [1]. Temperature variation is a primary driver, especially in arid climates where large diurnal ranges cause thermal stress and exfoliation [t1][t5]. However, Statement II is not the correct explanation for Statement I because the in-situ nature of weathering (Statement I) is a defining spatial characteristic of the process itself, whereas temperature variation (Statement II) is merely one of several specific causal mechanisms, alongside frost action, salt crystallization, and pressure release [c1][t8].

Sources

1. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > WEATHERING > p. 40
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Physical Weathering Processes > p. 83