The sedimentary rock most susceptible to chemical weathering by acid rain is limestone.

Here's why:

* Composition: Limestone is primarily composed of calcium carbonate (CaCO3).

* Acid Reaction: Acid rain, which contains sulfuric acid (H2SO4) and nitric acid (HNO3), reacts with calcium carbonate in a process called carbonation. This reaction produces calcium ions (Ca2+), bicarbonate ions (HCO3-), and water (H2O).

* Dissolution: The reaction effectively dissolves the limestone, leading to its breakdown and weakening.

While marble is a metamorphic rock, it is essentially a recrystallized form of limestone. Therefore, it shares the same vulnerability to acid rain as limestone.