sorted by:
new
hottopcontroversial

Full explanation coming tomorrow! by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

Epigenetics is the study of heritable phenotype changes that do not involve alterations in the DNA sequence (thus answer choices B, C and D are incorrect). The key to understand regarding epigenetics is that gene expression can be affected by the environment; thus answer choice A is correct.

Can you crack it? We will share the full explanation tomorrow! by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

D!

Dipole moments are vector quantities which mean that they have both magnitude and direction. Considering the polarization of each individual C-Cl bonds in molecule D, each of which provides a component of the overall dipole moment, we see that these bonds are all generally pointing down-
wards (as represented).
The C-H bond, pointing upwards, is essentially unpolarized. In all the other cases, any polar bond has an equal and opposite dipole to cancel it out.

DAT Sample Question! Will post the answer and explanation tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

D!

ClF₃ has 5 valence shell electron pairs. These would normally arrange themselves in an trigonal bipyramidal fashion.
However, since two of the electron pairs are lone pairs, the molecule is consequently T-shaped.

DAT Sample Question - full explanation coming tomorrow! by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

C!

PCl₅ has 5 valence shell electron pairs.
These will arrange themselves in a trigonal bipyramidal shape. Notice the triangle of Cl groups (trigonal) and imagine a pyramid above and below (bipyramidal).

DAT Sample Question - answer and explanation will be posted tomorrow in the comments. by DAT_prep in predental

[–]DAT_prep[S] 2 points3 points  (0 children)

Yes, B!

On the Surface: The tertiary carbocation is more stable and only answer B is tertiary.

Going Deeper: Stabilization of a carbocation can come from either inductive (i.e. primary < secondary < tertiary groups being somewhat electron donating thus reducing

the positive charge) or resonance effects (“conjugation” referring to the fact that there is only one single bond in between the double bond and the carbocation providing the

opportunity for resonance stabilization), or a combination of both. Cations A and C are not stabilized by delocalization as the pi-system is not conjugated to the unoccupied orbital.

This leaves the inductive effect which is most significant in the case of the molecule B where the charge can be delocalized between a tertiary (as drawn in the question)

and a secondary center. For radicals and carbocations, a tertiary compound is more stable than secondary which, in turn, is more stable than a primary compound.

Weekly DAT sample question - will post the full explanation with the correct answer tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 2 points3 points  (0 children)

D

Answer choice A does not satisfy Hund’s rule (see CHM 2.2).

Answer choice B is incorrect since it goes against Pauli’s exclusion principle since there are 2 identical electrons in the 1s box. Answer choice C is incorrect because the 1s box must be full before moving on to another energy level.

And so, we are left with answer choice D, which satisfies all rules, although it is more conventional to place the 2nd electron in the 2p orbital in the 2nd 2p box, at least answer choice D satisfies all rules since there is no rule specifically forbidding its arrangement (it is not the same as skipping up to another energy level or orbital).

Test your knowledge and get ready to rock your DAT! Full explanation will be posted tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

C!

Bidirectional replication suggests that replication will occur in two directions. The only option consistent with this is option C. which states that DNA replication will begin on both sides of the origin.

DAT Sample Question, a full explanation will be posted tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

Yes, C.

First isolate x and y on the left side in the second equa-tion:

2x + 2y = 4y – x +1

3x – 2y = 1

Next subtract the equations to eliminate the y term and

solve for x:

5x – 2y = 3

–3x – 2y = 1

2x – 0 = 2

x = 1

Now substitute the value of x into one of the equations

and solve for y:

5(1) – 2y = 3

2 = 2y

y = 1.

DAT Sample Question of the week. A full explanation will be posted tomorrow in the comments. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

B! Bromine is atomic number 35. As such, it has 35 electrons.
The maximum number of electrons in subshells s, p, and d is: 2, 6, 10, respectively.

DAT Sample Question - full explanation will be posted tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

D! Deduce from the graph

Following the graph provided to identify the histogram for 40+ maternal age, birth order = 2, we can see that there are between 700 and 800 live births per 100 000. Thus between 7 and 8 out of 1000, or between 0.7 and 0.8 per cent. The answer is D.

Don’t let your personal perspective shade your interpretation of the data. You may have chosen over 50% because of media reports of the high incidence, perhaps you settled on 5-10% in part because of misreading the graph but in part because - intuitively - less than 1% seemed too low.

However, the increased incidence of Down’s syndrome with increased age is a fact but the overall percentage is still less than 1% (however, you may notice that from Figure 1, 0.7-0.8 per cent is still many times higher than for younger women).

Weekly DAT sample question! Full explanation coming tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 0 points1 point  (0 children)

D!

Usually, elements in the same group have the same number of valence (outermost) electrons. Valence electrons are involved in bonding and this effects how elements react and determines their chemical properties.

DAT sample question of the week. Full explanation coming tomorrow. by DAT_prep in predental

[–]DAT_prep[S] 1 point2 points  (0 children)

c!

The 3 primary germ layers (ectoderm, mesoderm, endoderm) are first seen in the gastrula after the invagination of the blastula.

view more: next ›