D is correct. Metallic bonding.

A is wrong as it is a gross generalisation.

There are many exceptions and non-metal/non-transition metal catalysts.

One example is the use of phosphoric acid (H3PO4) in the hydration reaction of ethene to ethanol (electrophilic addition reaction)


https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Catalysis/Examples/Examples_of_Catalysis/4._Examples_of_Acid_Catalysis_in_Organic_Chemistry

https://courses.lumenlearning.com/introchem/chapter/homogeneous-catalysis/

Concentrated sulfuric acid is one catalyst which is not classified as “transition metal”.

Conc H2SO4 is not even metallic, let alone a transition metal/ compound formed with a transition metal

thx :) but why isnt B correct? based on "periodic table" chapter transition elements form coloured compounds tho

Read the option again.

'All coloured compounds contain transition elements'.

Once again, it is a sweeping statement and is false.

The option isn't 'all transition elements form coloured compounds', which has a different meaning.


Some analogies would be :

'all squares are rectangles, but not all rectangles are squares'
'All rectangles are parallelograms but not all parallelograms are rectangles'

It's a case of which is a subset of which (reminds you of E Math's Sets topic)

Some counter-examples :

Nitrogen dioxide gas (NO2) is a reddish-brown compound.

Aluminium iodide hexahydrate (AlI3.6H2O) usually exists as a yellow powder, but aluminium is not a transition metal.

thanks Mr J and Mr Eric! sorry for the late reply as i was quite burnt out from o level preparation...
do you have any tips for section B pure chemistry questions, the questions given are usually out of syllabus and hence i find them difficult to do, some are even A level questions. i usually lose marks in section B

also, is there any recommended ways to cope with the stress and burn out from the o level preparations... its holding me back from revising the past few months

Section B questions : try the top school papers to build familiarity. The questions are very conceptual so they test your understanding, rather than rote memorisation.

Look for the gist/essence of what the question is asking for, rather than simply reproducing what you have memorised.

It's all ' thinking questions' nowadays.

Stress is something that you experience because of some pressures you face.

You'll have to ask yourself, what is your goal for O levels? What is your expectation and what plans do you have for the future? Which school/institution are you aiming for?

If you meet those expectations, what's in it for you? If you don't, what is the worst that can happen?


Managing expectations will help to reduce the stress. Changing perspective helps too. Try to view O levels as just a rite of passage in your life.

Life is more than just studying or aceing/passing exams.


As for revising and burnout issues, it is better to do multiple alternating short periods of study (eg. 45 min) followed by rest/recreation (20-30 min, short naps, some internet surfing, games) than long study sessions followed by long breaks.

Keeps your momentum up that way and doesn't tire you as much.

It depends on LockB’s strength though.

Some of my N and O Level students who are taking combined Science (even those are not under my wing for Chem) are already struggling with their conceptuals, so for such students, giving them thinking questions might backfire.

The Section B ones you would have to try and circumvent the words. These go beyond O Levels and you must use the information given as closely as you can.

For top school papers, the whole point is to study the question types and look at the answer keys since there isn't much time left to O levels. i.e get the gist of what they're asking for

The issue is as LockB says, he/she is already finding current section B questions difficult so there's no point trying to do just easy/basic concepts for section B papers.

Those conceptual stuff /simpler questions should already been covered in notes or worksheets. He/she will have to revise those first then go on to the tougher ones.


How much could it backfire like you mention, if at the O levels he's going to get the same 'out of syllabus' questions anyway.


The whole idea is to translate whatever concepts that have been taught to the exam hall, along with the act of integrating/applying across different topics for the questions.

Anyway LockB, if you find these difficult to do by yourself then I strongly recommend you to get a tutor for the last leg of your revision before the O levels.

You can check with Eric if he has any vacancies or slots and if he's willing to tutor you.

i've done the 2020 and 2019 papers, some of the section B questions are manageable but there is one which is more difficult to understand (the one on de-icers, 2020 paper). it is said that the papers will be more difficult like the 2020 paper since organic chemistry is not tested anymore but not sure if its true

my school's prelim paper and some other top school papers are tougher to understand...

That's very normal. These questions are usually the ones that separate the A1s from the A2s

Can I know your expected grades for O levels?

aiming to get A1 for chemistry, but i usually get a low A2 for school exams. got A2 this time
A1 for emath, got A1 for school exams (80+)
A1 for amath, got A2 for school exams (could have gotten A1 if not for careless mistakes)

but i heard the bell curve for these subjects will pull the A1 up to 80+,especially for math...

Sounds like you're on the right track.

Not exactly a bell curve, but more of a grading profile.

Usually we'll aim for 90 to secure the A1 for math.

The bell curve has been removed though…

But I’m pretty certain they use something similar for grading purposes.

It is not a bell curve per se. There was never any bell curve anyway. The scores are referenced against a set of standards.

https://www.sutd.edu.sg/About/happenings/News/2019/6/No-bell-curve-grading-in-national-exams

thx :) for emath, when they say "find the highest common factor", are we supposed to write in index form or write the obtained value?
eg 2² x 3 x 11 or 66

To play safe, if they do not include “in index notation”, I calculate it.

Also, some things like

“write the chemical formula of…”

and

“name the substance”

must be treated differently

Find the HCF → number
Find the HCF and leave your answer index notation → __ × __ × __

chemical formula = Ca(OH) 2
chemical name = calcium hydroxide
is this correct?

for qualitative analysis questions when can we write the formula and when can we not?

Yes.

You'll need to see the phrasing of the question

what is the difference between percentage change/increase/decrease? like are they calculated the same way or percentage change is calculated differently from the other two?

“Change” is more of an absolute measure, so it is usually taken to be positive.

Otherwise, they are all the same

Change means either a positive or negative.

It is not a modulus.


Eg. Old price $100, new price $90

Percentage decrease = (100 - 90) / 100 × 100 %
= 10/100 × 100%
= 1/10 × 100
= 10%


BUT percentage change here = -10%


It is the the same idea as rate of change.

You can say the radius of a balloon is decreasing at 1cm/s for example.

Rate of change = -1cm/s

Essentially, percentage change


= (Final value - Initial value) /|initial value| × 100%

| | means modulus or absolute value.

It would be counted as identical to percentage increase though.

When a number is “changed” by 2, for example, it can mean the addition to or the subtraction of 2 from the number.

Or we can say like

John had $100.
A few minutes later, John’s money changed by $10.
How much money did John have in the end?

It could be a change for the better…or it could be a change for the worse.

What you were actually describing is called 'percentage difference'

So no, it is not percentage change.


The rate of change is a very clear analogy.

In physics it's the same case.

A car slowed down from 50km/h to 30km/h while travelling forward.

Its velocity decreased by 20km/h.

Its velocity increased by -20km/h

Change in speed/velocity = -20km/h


The change here comes with the sign. It is not like how it is used in the linguistic sense.

The sign indicates whether it is positive (increase) or negative (decrease)

Additional point by the way :

Your example shows that the info given is vague i.e it only states change by $2 but doesn't tell if the change is positive or negative.

So due to lack to information , it cannot be solved i.e there is no 1 definite answer.



But for the question style that LockB's asked, you are actually supposed to find the change (and it is solvable and to be determined)

So its a matter of whether it's a positive or a negative change.

If positive, the value is positive.

eg. There is an 83⅓% change in sales revenue (though usually in financial markets and lingo there will be a +) OR the change in sales revenue is 50%


If negative, the value is negative.

eg. There is a -50% change in the number of toys OR the change in the number of toys is -50%.



Putting the sign is in a sense, to be specific about the direction of the change , while sparing the need to use terms like 'increase', 'decrease', 'rose' 'fell', 'gone up' and 'slipped down', of which the direction is already implied.