<u>Answer:</u>
Carbon and silicon both are tetravalent elements as compared to germanium, tin, and lead which are divalent.
That's because Ge, tin, and Pb show inert pair effect and has a greater nuclear effective charge on the 's' electrons due to poor shielding effect. .That's why these elements are not able to share their valence electrons while carbon and silicon does and show "catenation" which is the ability to form long chain molecules.
A. If an objects velocity is decreasing, the object is said to be decelerating not accelerating.
B. If an objects velocity changes, it is either experiencing acceleration or deceleration
C. If an object is said to be decelerating, its velocity must be decreasing.
D. If an objects velocity remains constant, its acceleration is zero.
∴ B is correct
