Answer:b.CaCl2
Explanation:
A compound is a substance resulting when two or more elements are are chemically bonded together either ionically or covalently in a fixed ratio.
From the given options we can see that the only compound there is CaCl2 which is an ionic compound in the fixed ratio of one calcium ion to two chloride ions.
Other options , Cu,Na and Nd are merely pure substance---Elements
Answer:
Molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break. Molecules must collide with the proper orientation. A collision that meets these two criteria, and that results in a chemical reaction, is known as a successful collision or an effective collision.
Temperature can change a reaction rate because adding or taking away heat means energy is being added or taken away. When energy is added, the particles speed up, so there is a greater chance of the reactants colliding to form the products, which increases the reaction rate. When energy is taken away, the particles more slower, so they don't collide as easily, which slows down the reaction rate.
Therefore, the answer is D.
