Question

what is involved in weathering?
volcanoes
water
seafloor spreading
mountain building

Explanation:

Weathering is the process of breaking down rocks. Water is a key agent in weathering (both mechanical, like freeze - thaw, and chemical, like dissolution). Volcanoes are related to igneous activity and not directly to weathering. Seafloor spreading is a plate - tectonic process for creating new oceanic crust. Mountain building is a tectonic process of rock uplift, not weathering. So water is involved in weathering.

Answer:

water