Identify compound $Z$ and the directing effects

From the statement, $Z$ is a phenolic aromatic compound containing a tert-butyl group. For such a ring:

• The phenolic group $(-OH)$ is a strong activating, ortho/para-directing group due to its $+M$ (resonance donating) effect.
• The tert-butyl group is an alkyl group, also ortho/para-directing by hyperconjugation/$+I$ effect, but its most important contribution here is often steric hindrance because it is bulky.

Nature of halogenation of phenols

In electrophilic substitution of phenols with halogens:

• The ring is strongly activated by $-OH$.
• Hence substitution occurs readily at positions activated by the phenolic group.
• However, the actual position and extent of substitution depend on both:
  • electronic activation/directing effects, and
  • steric accessibility of positions.

Examine the given explanations one by one

Option C: electronic effect of the phenolic group

This is definitely important.

The $-OH$ group donates electron density to the ring by resonance: $\ce{-OH -> ring}$ making the ortho and para positions highly reactive toward electrophiles such as $\ce{Cl+}$, $\ce{Br+}$, etc.

So, Option C is correct.

Option B: steric effect of the tert-butyl group

The tert-butyl group is very bulky. Even if a position is electronically favored, approach of the electrophile to nearby positions can be hindered.

Therefore, differences in substitution pattern can certainly be explained by steric hindrance from the tert-butyl group.

So, Option B is correct.

Option A: steric effect on the halogen

Different halogens have different sizes: $\ce{F < Cl < Br < I}$ Larger halogens face greater steric difficulty in approaching crowded positions on the aromatic ring.

Thus, the pattern of substitution changing with different halogens can be explained partly by the steric size of the halogen electrophile.

So, Option A is correct.

Option D: electronic effect of the tert-butyl group

Although tert-butyl is weakly electron donating by $+I$/hyperconjugation, this effect is much weaker than the phenolic $+M$ effect and generally does not explain the observed special pattern of halogen substitution in such questions. The key role of tert-butyl here is steric, not electronic.

Hence, Option D is not taken as a correct explanation.

Final selection

The observed electrophilic substitution pattern is explained by:

• steric effect on the halogen,
• steric effect of the tert-butyl group,
• electronic effect of the phenolic group.

Therefore, the correct options are: $\boxed{A,\ B,\ C}$

Comparison with stored answer

Stored correct answer: $A, B, C$

Derived answer: $A, B, C$

These match exactly.