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: $CH_{3}CH_{2}CH(OH)CH_{2}CH_{3}$

• $CH_{3}CH(OH)CH(CH_{3})_{2}$ 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: quantum shells

• Atoms: This is incorrect because atomic emission spectroscopy does not provide evidence for the existence of atoms.
• Electrons: This is incorrect because atomic emission spectroscopy does not provide evidence for the existence of electrons.
• Isotopes: This is incorrect because the evidence for isotopes is provided by mass spectroscopy.

Sorry, that is incorrect.

The only correct answer is: $Na^{+}$ and $Mg^{2+}$

• $N^{3-}$ and $Cl^{-}$ is incorrect because the chloride ion has an extra shell of electrons compared to the nitride ion.
• $O^{2-}$ and $S^{2-}$ is incorrect because the sulfide ion has an extra shell of electrons compared to the oxide ion.
• $Na^{+}$ and $K^{+}$ is incorrect because the potassium ion has an extra shell of electrons compared to the sodium ion.

Sorry, that is incorrect.

The only correct answer is: Be, Rb, Ba and Ra

• Li, Na, Mg, and Cl is incorrect because Chlorine is in group 7 and therefore a p-block element.
• K, Ca, Co, and Rb is incorrect because Cobalt is a transition element and therefore a d-block element.
• Mg, Al, Sr, and Ba is incorrect because Aluminum is a group 3 element and therefore a p-block element

Sorry, that is incorrect.

The only correct answer is: poor electrical conductivity

• a high melting temperature is incorrect because both graphene and graphite are similar to diamond in having a high melting temperature
• a precise molecular formula is incorrect because neither graphene nor graphite nor diamond have a precise molecular formula since they are giant molecular structures
• a giant structure is incorrect because graphene, graphite, and diamond are all giant molecular structures.

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: $CO_{2}$

• $H_{2}S$ is not correct because it has a similar shape to water.
• $SO_{2}$ is not correct because it has a trigonal planar shape, resulting from the lone pair and two groups of electrons in the two double bonds.
• $CH_{2} = CH_{2}$ is not correct because it is planar but not linear.

Sorry, that is incorrect.

The only correct answer is: All at 120$^\circ$

• 90$^\circ$ and 109.5$^\circ$ is not correct because the angles within a layer of graphite and graphene are neither 90$^\circ$ nor 109.5$^\circ$ but are all 120$^\circ$
• All at 109.5$^\circ$ is not correct because the angles within a layer of graphite and graphene are not 109.5$^\circ$ but are all 120$^\circ$
• 109.5$^\circ$ and 120$^\circ$ is not correct because there are no angles within a layer of graphite and graphene that are 109.5$^\circ$ but they are all 120$^\circ$

Sorry, that is incorrect.

The only correct answer is: giant ionic