Hemoglobin contains $$0.34 \%$$ of iron by mass. The number of Fe atoms in $$3.3 \mathrm{~g}$$ of hemoglobin is

(Given: Atomic mass of Fe is $$56 \,\mathrm{u}, \mathrm{N}_{\mathrm{A}}=6.022 \times 10^{23} \mathrm{~mol}^{-1}$$.)

Arrange the following in increasing order of their covalent character.

A. $$\mathrm{CaF}_{2}$$

B. $$\mathrm{CaCl}_{2}$$

C. $$\mathrm{CaBr}_{2}$$

D. $$\mathrm{CaI}_{2}$$

Choose the correct answer from the options given below.

Class XII students were asked to prepare one litre of buffer solution of $$\mathrm{pH} \,8.26$$ by their Chemistry teacher: The amount of ammonium chloride to be dissolved by the student in $$0.2\, \mathrm{M}$$ ammonia solution to make one litre of the buffer is :

(Given: $$\mathrm{pK}_{\mathrm{b}}\left(\mathrm{NH}_{3}\right)=4.74$$

Molar mass of $$\mathrm{NH}_{3}=17 \mathrm{~g} \mathrm{~mol}^{-1}$$

Molar mass of $$\mathrm{NH}_{4} \mathrm{Cl}=53.5 \mathrm{~g} \mathrm{~mol}^{-1}$$ )

At $$30^{\circ} \mathrm{C}$$, the half life for the decomposition of $$\mathrm{AB}_{2}$$ is $$200 \mathrm{~s}$$ and is independent of the initial concentration of $$\mathrm{AB}_{2}$$. The time required for $$80 \%$$ of the $$\mathrm{AB}_{2}$$ to decompose is

Given: $$\log 2=0.30$$ $$\quad \log 3=0.48$$