75,000 particles
35,000 particles
25,000 particles
50,000 particles
Correct answer is C
Given:
t\(\frac{1}{2}\) = 20 years
After the first 20 years, half of the substance (\(\frac{1}{2} \times 100,000 = 50,000\)) will have decayed. Hence, we have 100,000 - 50,000 = 50,000 particles left.
After the second 20 years (being 40 years in all), half of the remaining substance (\(\frac{1}{2} \times 50,000 = 25,000\)) will have decayed.
Remaining particles after 40 years = 50,000 - 25,000
= 25,000 particles.
5
7
3
9
Correct answer is C
Methyl orange is the best indicator for the reaction with range 3.1 - 4.4.
The molecular shape and bond angle of water are respectively
linear, 180°
bent, 109.5°
tetrahedral, 109.5°
bent, 105°
Correct answer is D
The shape of water molecule = Bent/ V- shaped The bond angle of water = 104.5°/ 105°
ii and iii only
ii and iv only
iii and iv only
i and ii only
Correct answer is B
Ionization energy and electron affinity increase across a period, and decrease down a group.
2.0 moldm\(^{-3}\)
0.25 moldm\(^{-3}\)
1.0 moldm\(^{-3}\)
0.5 moldm\(^{-3}\)
Correct answer is A
Given the Mass of the salt = 58.5g
Volume = 250 cm\(^3\) = 0.25 dm\(^3\)
Mass concentration = \(\frac{Mass}{Volume}\)
= \(\frac{58.5}{0.25}\) = 234 gdm\(^{-3}\)
Solubility (in moldm\(^{-3}\) = \(\frac{234}{111} \)
= 2.11 moldm\(^{-3}\)
\(\approxeq\) 2.0 moldm\(^{-3}\)
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