Chemistry

1.20. The values after round up with three significant figures are:

(i) 34.2

(ii) 10.4

(iii) 0.0460

(iv) 2810

1.19. The significant figures in the given values are:

(i) 2 in 0.0025

(ii) 3 in 208

(iii) 4 in 5005

(iv) 3 in 126,000

(v) 4 in 500.0

(vi) 5 in 2.0034

1.18. The scientific notation of the given values are:

(i) 4.8*10^?3

(ii) 2.34*10⁵

(iii) 8.008*10³

(iv) 5.000*10²

(v) 6.0012*10⁰

1.17. 15 ppm means 15 parts per million i.e.15 in 10⁶

So, % by mass = 15/10⁶ x 100 = 15 x 10^-4 = 1.5 x 10^-3%

Molality = No. of moles of solute/Mass of solvent in kg

Percent by mass = 1.5 x 10^-3 % means 100 g of the sample contain 1.5 x 10^-3 g chloroform.

So, 1000 g or 1 kg of the sample will contain 1.5 x 10^-3 x 1000/100 = 1.5 x 10^-2 g chloroform.

Molar mass of chloroform = 12 + 1 + (3 x 35.5) = 119.5 g/mol

Therefore, molality = 1.5 x 10^-2 /119.5 = 1.26 x 10^-4m.

1.16. Significant figures are meaningful digits which are known with certainty plus one which is estimated or uncertain. The uncertainty in the experimental or the calculated values is indicated by mentioning the number of significant figures

1.15. micro = 10^–6, deca = 10, mega = 10⁶, giga = 10⁹, femto = 10^–15

Hydrolysis of aikyltrichlorosilanes gives cross-linked silicones.

Due to inert pair effect, elements of group 14 exhibit oxidation states of +2 and +4. Thus, option (b) is correct.

Thermodynamically the most stable form of carbon is graphite, i.e., option (b) is correct.

In B₂H₆, B is sp³-hybridized. Therefore, option (c) is correct.