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- Bold 1: Poor leading sentence. Ozone depletion is caused by various substances not only CFC's which is what you implied - Red: Useless - Bold 2: Poor cause and effect (I know what you're trying to say, but it's not simply that free radicals directly cause ozone depletion) - Overall: Poor...

You can use either (I've seen both in exam solutions that were awarded marks). For your second Q, draw in boiling chips if you are using the Bunsen burner (this allows the reactants to heat evenly to prevent "spitting")

Which answers? Do you have source

Q: Prove tan x > x for 0 < x < pi/2 Am I allowed to just graph the two and show it? My only problem with this method is that it is not really proving it (if I didn't know better, I could have just purposely constructed the two graphs such that tan x > x since I know that's what the question wants)

I've heard of people making it up

If NaHCO3 precipitates how can it be in (aq) :P My teacher always emphasised having the correct states for this dot point and she was a previous HSC marker so I assume they are "fussy". BTW this is the full equation: NaCl(aq)+CO_2(g)+H_2 O(l)+NH_3(aq)→NaHCO_3(s)+NH_4 Cl(aq)

Yeah I thought so hahaha :) The same points would still apply: Pro's of hydroxide vs. carbonate: MORE Mg2+ precipitated, and other impurities (iron ions) precipitated

MgCO3 is "slightly soluble" (although not much. Yes you could be fine with using carbonate as you said but the aim is to soften it as much as possible) hence we precipitate with hydroxide to Mg(OH)2 which is very insoluble. If we're talking about water purification in general instead of focusing...

I guess all the math enthusiasts ending up doing 4U

Looks like this will fill up very fast...

Not only do surfactants reduce the surface tension of a liquid it is dissolved in, it reduces the interfacial tension between two liquids to allow them to better mix.

state rank

You need to also highlight in your answer how to specifically produce transuranic elements (note that Z = 93,94,95 have a different method of production than Z = 96+)

Yeah both of you guys missed the whole point of "transuranic"

I don't like how you have +-sqrt 5 as zeros to consider, because that thereom only applies to integer zeros (if I recall correctly) - it feels like you only listed it because you saw the answer. For safety just expand the polynomial and factorise (x+2). Doesn't take that long anyway

What did you do here? Sorry I don't follow

Re: HSC Physics Marathon 2014 read the q pls

Really? I just googled it and first thing that comes up for pure substance is a substance consisting of only one type of element or molecule

Wow never heard of this rule... Can I ask where the question is from OP? I wonder if HSC has had a similar Q

Is this before or after the HSC?