Atoms And Molecules

The number of water molecules present in one formula unit of gypsum is 2.

✅ Correct answer: 2

Explanation: The chemical formula of gypsum is CaSO₄·2H₂O, which means each formula unit of gypsum contains 2 water molecules of crystallization.

Cyclopentane is a cyclic hydrocarbon with five carbon atoms in a ring. Each carbon atom forms two single bonds with adjacent carbons and two single bonds with hydrogen atoms. The general formula for a saturated cyclic hydrocarbon with carbon atoms is . For :

Final Answer: The molecular formula of cyclopentane is , which corresponds to option .

Bond length is the distance between the nuclei of two bonded atoms. It generally increases as the size of the atoms involved in the bond increases. In this case, all the molecules involve hydrogen ( ) bonded to a halogen ( ). The size of the halogen atom increases down the group in the periodic table due to the addition of electron shells.

Among the halogens, iodine ( ) is the largest atom, followed by bromine ( ), chlorine ( ), and fluorine ( ). Consequently, the bond length of is the longest, as the larger iodine atom results in a greater distance between the hydrogen and iodine nuclei.

Final Answer: The molecule with the highest bond length is , which corresponds to option .

Methane consists of a central carbon atom bonded to four hydrogen atoms. The carbon atom undergoes hybridization, where its one orbital and three orbitals mix to form four equivalent hybrid orbitals. These hybrid orbitals are directed towards the corners of a regular tetrahedron, with bond angles of approximately .

The tetrahedral arrangement minimizes electron pair repulsion, as predicted by VSEPR (Valence Shell Electron Pair Repulsion) theory. This results in a symmetrical tetrahedral shape for the methane molecule.

Final Answer: The shape of the methane molecule is , which corresponds to option .

A nitrogen molecule consists of two nitrogen atoms bonded together by a triple bond. A triple bond is composed of one sigma ( ) bond and two pi ( ) bonds. The bond is formed by the head-on overlap of atomic orbitals, while the bonds are formed by the lateral overlap of p-orbitals.

In , each nitrogen atom contributes three electrons to form the triple bond, satisfying the octet rule for both atoms. This results in one bond and two bonds.

Final Answer: The covalent bonds in a nitrogen molecule consist of , which corresponds to option .

The molecular structure of (ethyne or acetylene) involves a triple bond between two carbon atoms. This triple bond consists of one sigma bond and two pi bonds. Additionally, each carbon atom is bonded to one hydrogen atom with a sigma bond. Thus, in :
There are 3 sigma bonds: 1 between the two carbon atoms, and 2 between each carbon and hydrogen.
There are 2 pi bonds in the triple bond between the carbon atoms.

The correct option is (B): 3 sigma and 2 pi

In the water molecule , the oxygen atom forms two single bonds with two hydrogen atoms. The oxygen atom also has two lone pairs of electrons. The oxygen atom's electron configuration is , and it undergoes hybridization with one orbital and three orbitals, resulting in hybridization. This leads to a bent shape with a bond angle of approximately 104.5°, due to the repulsion between the lone pairs and bonding pairs. Thus, the hybridization in molecule is .

The correct option is (A):