A tert-butyl functional group is electron donating and will therefore activate the ortho and para positions. However, the ortho positions are sterically hindered by the bulky tert-butyl group. Therefore, the para position will be favored. 

In the molecule shown, the nitro group will direct incoming substituents to positions meta to it, and the methoxy group will direct incoming substituents ortho or para to it. The only product option shown in which the chlorine substituent is meta (1,3) to the nitro group AND either ortho (1,2) or para (1,4) to the methoxy group is option I.

In the molecule shown, the aldehyde group will direct incoming substituents to positions meta to it, and both the the hydroxyl group AND the fluorine group will direct incoming substituents to positions ortho or para to them. Options I and III show the incoming substituent meta to the aldehyde group, as well as either ortho or para to both the fluorine group and hydroxyl group. Therefore, they are both possible products.

Note: because option III shows attachment at a carbon that is slightly less sterically hindered than that of option I, option III will be produced in a slightly greater quantity.

The reagents shown will add a bromine to an aromatic ring through an electrophilic aromatic substitution mechanism. A nitro  group is a strong electron withdrawing group and a benzene deactivator. All benzene deactivators (with the exception of halogens) direct incoming substituents to the meta  positions. Therefore, option III is the major product.

This is an example of a Friedel-Crafts acylation reaction, which will add an acyl group (alkyl group containing a carbonyl () group) to a benzene ring at the carbonyl carbon (shown below).

This reaction proceeds using an electrophilic aromatic substitution reaction mechanism. The presence of the hydroxyl group on the benzene will affect where the incoming acyl group will attach. A hydroxyl group is a strong benzene activator, which will direct incoming substituents to positions ortho  or para  to it. Option I is the only option shown where the incoming substituent is attached at either the ortho or para position.

This reaction proceeds using an electrophilic aromatic substitution reaction mechanism. The presence of the amino group on the benzene will affect where the incoming acyl group will attach. An amino group is a strong benzene activator, which will direct incoming substituents to positions ortho  or para  to it. Option III is the only option shown where the incoming substituent is attached at either the ortho or para position on a benzene ring.

Several resonance structures can be drawn for the molecule phenol. These are shown below.

Because the overall charge distribution puts partial negative charges on carbons , , and , these carbons have an increased nucleophilic character. Therefore, these carbons are more likely than the other carbons to accept an incoming electrophilic substituent, making these positions more likely to be substituted. Carbons  and  are known as the ortho positions, and carbon  is known as the para position.

Several resonance structures can be drawn for the molecule nitrobenzene. These are shown below.

From these resonance structures, an overall molecular electronic distribution can be determined:

Because the overall charge distribution puts partial positive charges on carbons , , and , these carbons have an increased electrophilic character. Therefore, these carbons are less likely than the other carbons to accept an incoming electrophilic substituent, making these positions less likely to be substituted. By default, carbons , and , known as the meta positions are the only ones nucleophilic enough to carry out this reaction.

When speaking of the arrangemts of two substituents on a benzene, their positions can be ortho, meta, or para. Ortho substituents are bound to adjacent carbons (C1 and C2). Meta substituents are bound to carbons with one intermediary carbon (C1 and C3). Para substituents are opposite one another across the benzene ring (C1 and C4).

The bromines in the given reaction result in a para product because bromine is ortho/para directing. There is a significant amount of ortho product, but because of steric hinderance, the major product is para.

This question is essentially testing an understanding of electrophilic aromatic substitution and substituent placement.  first acts as a lewis acid by accepting the chloride from the  reagent, which generates . This, in turn, is susceptible to nucleophilic attack from one of the double bonds in the benzene ring. Due to the disruption of aromaticity in the ring, this double bond is quickly restored by abstraction of an adjacent proton on the ring.

But we also need to be aware of what position this substituent will be directed to. Since the original molecule, toluene, consists of a benzene ring bonded to an electron-donating methyl group, this directs the substitution reaction towards the ortho or para position on the ring. Of the choices shown, only the para position is shown. The ortho position is not shown as an answer choice, and direction to the meta position would not be likely.