CAIE Oct/Nov 2019 session discussion

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Hey ! My friends call me Queen or Queenie first and foremost.

I'm here to ask around if people can help me figure out and wrap my head around Chemistry As Level MCQ... I'm so bad at it and it hurts because Practicals and Structured Questions are a cakewalk comparatively.

Any suggestion and tip goes a long way, thanks in advance !
Don't worry it's perfectly normal. i'm not to good at it either.the key to passing MCQs is to practice as many as possible.test yourself and time yourself you will see some results if you keep doing this.you can also buy this book called 1000 A level chemistry MCQ's by Redspot.it's really good it has mcq's from all the As topics and there are exam favorite ratings attached to the questions which tell you the likelihood of them being asked
 
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The reaction between sulfur dioxide and oxygen is reversible.
2SO2(g) + O2(g) 2SO3(g) Kc = 280 mol–1 dm3 at 1000K
In an equilibrium mixture at 1000K the sulfur trioxide concentration is 6.00mol dm–3.
The sulfur dioxide concentration is twice the oxygen concentration.
What is the sulfur dioxide concentration?
A 0.175 mol dm–3
B 0.254 mol dm–3
C 0.318 mol dm–3
D 0.636 mol dm–3

I need the explanation and full method please..(THE ANSWER IS D)
 
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Two reactions and their enthalpy changes are shown.
2C(s) + 2H2(g) → C2H4(g) ∆Ho = +52.2 kJ mol–1
C2H2(g) + H2(g) → C2H4(g) ∆Ho = –175.8 kJ mol–1
These data can be used to calculate the enthalpy change for the reaction shown.
2C(s) + H2(g) → C2H2(g) ∆Ho= X
What is the value of X?
A –228.0 kJ mol–1
B –123.6 kJ mol–1
C +123.6 kJ mol–1
D +228.0 kJ mol–1

I need the full method please...(THE ANSWER IS D)
 
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