How many of the following molecules / ions have a trigonal planar structure?
\( \text{BO}_3^{3-}, \, \text{NH}_3, \, \text{PCl}_3, \, \text{BCl}_3, \, \text{ClF}_3, \, \text{XeO}_3 \)
A block of certain mass is placed on a rough floor. The coefficients of static and kinetic friction between the block and the floor are 0.4 and 0.25 respectively. A constant horizontal force \( F = 20 \, \text{N} \) acts on it so that the velocity of the block varies with time according to the following graph. The mass of the block is nearly (Take \( g = 10 \, \text{m/s}^2 \)):
Such a group of atoms is called a molecule. Obviously, there must be some force that holds these constituent atoms together in the molecules. The attractive force which holds various constituents (atoms, ions, etc.) together in different chemical species is called a chemical bond.
There are 4 types of chemical bonds which are formed by atoms or molecules to yield compounds.