Litmus paper is used to determine if a substance is acid or an alkaline. So for this question you have to ask your self which one of the options are an acid or alkaline. 

i. SO4^-2 is neither an acid or base. 
ii. H3O^+ is in fact a hydrated hydrogen ion therefore it is an acid. 
iii. NH4^+ is an acid as it can release a H+ ion into solution 
iv. OH- is alkaline. 

Therefore, it can be between ii, iii and iv.   This is not an option given. So I order to eliminate further possible answer; for NH4^+ to be tested using litmus paper you would require NaOH as a reagent- ii and iv does not require this. So that cancels this out option iii. 

The answer is A.  

Definitions of:
-Acid: a substance that releases a H+ ion in solution. 
-Base: a substance that releases OH- ions in solution. 

Hopefully this makes sense, if not feel free to pop up and message me for further guidance! 

Maths

The following are chemical entities identifiable during qualitative analysis:
i. SO
2−
4

ii. H3O+
iii. NH
+
4

iv. OH−
Which of them can be detected by litmus paper?
Options
A) ii and iv only
B) ii only

C) i and iii only

D) iv

Lower Bound:
C = 404.5 mm
D = 125 mm 

Upper Bound:
C = 405.5 mm
D = 135 mm

Circumference is rounded to the nearest 1mm, therefore when working out the boundaries for that you do +/- 0.5 (half of 1)

Diameter is rounded to the nearest 10mm, therefore when working out boundaries for that you do +/- 5 (half of 10)

Hope this helps :) 

Helen draws a random circle. she then measure it diameter and circumference. should get a circumference, C, of 405mm correct to 3 significant figures she get a diameter, D, of 130mm correct 2 significant figures.  Lower and upper bound of C/D

Formula for compound interest:
original x multiplier^years

1.5% increase as a multiplier is 1.015 [you do 1 + (% x 100) as it’s % increase]

12000 x 1.015^2 = £12362.70

If you have any more questions- feel free to message me :) 


It I invest £12000 in a saving account the account pays 1.5% compound interest per year what is the value of her investment after 2 years

Hiya Elouise!
It mainly depends on what you would like to do at A Level to know how important of an effect this can have. However, some sixth form do give you the option of studying your chosen subject at A Level as long as you are able to continue and resit you’re Maths GCSE the consecutive year or next available chance. :)

Emi K

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