Sorry, that is incorrect.

The only correct answer is: no change

• orange to green is not correct because tertiary alcohol is not oxidized
• green to orange is not correct because this is an incorrect colour change for acidified dichromate
• purple to colourless is not correct because this is an incorrect colour change for these reagents.

Sorry, that is incorrect.

The only correct answer is: ions

• only carbocations is not correct because both anions and cations are produced
• only free radicals is not correct because homolytic fission produces free radicals
• free radicals and ions is not correct because homolytic fission produces free radicals and heterolytic fission also produces anions

Sorry, that is incorrect.

The only correct answer is: $CH_{3}CH_{2}CH(OH)CH_{2}CH_{3}$

• $CH_{3}CH(OH)CH(CH_{3})_{2}$ is not correct because it will not form pent-2-ene
• $CH_{2}(OH)CH_{2}CH_{2}CH_{2}CH_{3}$ is not correct because it will only form pent-1-ene
• $CH_{3}CH_{2}CH_{2}CH(OH)CH_{3}$ is not correct because $CH_{3}CH(OH)CH_{2}CH_{2}CH_{3}$ will also form Pent-1-ene

Sorry, that is incorrect.

The only correct answer is: 16 $\sigma$ bonds and 1 $\pi$ bonds

• 5 $\sigma$ bonds and 2 $\pi$ bonds is incorrect because there are 10 $\sigma$ C-H bonds, 6 C-C $\sigma$ bonds and 1 C-C $\pi$ bond
• 6 $\sigma$ bonds and 1 $\pi$ bonds is incorrect because there are 10 $\sigma$ C-H bonds, 6 C-C $\sigma$ bonds and 1 C-C $\pi$ bond
• 15 $\sigma$ bonds and 2 $\pi$ bonds is incorrect because there are 10 $\sigma$ C-H bonds, 6 C-C $\sigma$ bonds and 1 C-C $\pi$ bond

Sorry, that is incorrect.

The only correct answer is: free radical substitution.

• electrophilic addition is not correct because electrophilic addition would be the reaction mechanism between alkenes, such as ethene, and chlorine but the substance in the question is the alkane, ethane
• electrophilic substitution is not correct because electrophilic substitution involves the reactions of aromatic systems but this question refers to the reaction of the alkane, ethane
• free radical addition is not correct because the mechanism of reaction between an alkane such as ethane and chlorine involves substitution and not addition

Sorry, that is incorrect.

The only correct answer is: 12 

• 5 is incorrect because this is the number of electrons in the 3p orbitals of the chlorine atom
• 6 is incorrect because this is only the number of electrons in the 3p orbitals of the chloride ion
• 18 is incorrect because this is the total number of electrons in the chloride ion, not just those in the p orbitals.

Sorry, that is incorrect.

The only correct answer is: $Mn^{2+}$

• $Cr^{3+}$ is incorrect because it is $3d^{3}$ not $3d^{5}$
• $Fe^{2+}$ is incorrect because it is $3d^{6}$ not $3d^{5}$
• $Mn^{3+}$ is incorrect because it is $3d^{4}$ not $3d^{5}$

Sorry, that is incorrect.

The only correct answer is: acid-base 

• displacement is incorrect there Is no displacement taking place
• redox is Incorrect because neither substance is oxidized or reduced
• substitution is incorrect because there is no substitution taking place

Sorry, that is incorrect.

The only correct answer is: Fluoromethane ($CH_{2}F$)

• Hydrogen fluoride (HF) is not correct because fluorine is very electronegative and has a suitable lone pair of electrons for hydrogen bonding.
• Hydrogen peroxide ($H_{2}O_{2}$) is not correct because it has hydrogen bonding; compare with water.
• Methanol ($CH_{2}OH$) is not correct because alcohols can have hydrogen bonds; compare with water.

Sorry, that is incorrect.

The only correct answer is: anions and cations.

• atoms and delocalized electrons is incorrect because ionic bonding involves positive ions and negative ions
• cations and delocalized electrons is incorrect because there are no delocalized electrons in ionic bonding
• two nuclei and a shared pair of electrons is incorrect because this is a description of covalent bonding