Chemistry Questions & Answers - Free Online Practice

866.

The following arrangement of elements in order of decreasing number of outer electrons; One of the elements is wrongly placed. Which is it? ALUMINIUM, CHLORINE, SILICON, MAGNESIUM AND SODIUM.

chlorine

aluminium

silicon

magnesium

sodium

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Correct answer is B

No explanation has been provided for this answer.

867.

Which of the following represents a precipitation reaction?

H₂SO₄ + NaCl $\to$ NaHSO₄ + HCl

Fe +H₂SO₄ $\to$ FeSO₄ + H₂

4HCl + MnO₂ $\to$ MnCl₂ + 2H₂O + Cl₂

Na₂SO₄ + pb(NO₃) $\to$ PbSO₄ + 2NaNO

CuO +2HCl $\to$ Cl₂ + H₂O

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Correct answer is D

No explanation has been provided for this answer.

868.

1.00g of mixture of calcium carbonate and calcium oxide liberated 0.33g of carbon dioxide on strong heating. The percentage of calcium oxide in the mixture is? (Ca = 40, C = 12, O = 16)

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Correct answer is C

CaCO₃ + CaO $\to$ 2CaO + 2CO₂

44gm of CO₃ is liberated by 100gm of CaCO₃

0.33gm of CO₂ will be liberated by $\frac{100}{44}$ x 0.33

= 0.75 of CaCO₃

Amount of CaO = 1 - 0.75

= 0.25

% of CaO = $\frac{0.25}{1} \times \frac{100}{1}$

= 25%