Which one of the following cations gives a chocolate brown precipitate upon addition of aqueous solution of $\mathrm{K}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]$ ?
$\mathrm{Fe}^{3+}$
$\mathrm{Cu}^{2+}$
$\mathrm{Zn}^{2+}$
$\mathrm{Ca}^{2+}$
A compound contains two types of atoms $A$ and $B$ .Its crystal structure is a cubic lattice with'$A$' atoms at the corner of the unit cells and'$B$'atoms at the body centres.The simplest formula of the compound will be
$A_2 B$
$A B_2$
$A B$
$A B_3$
The plot of radial probability density( $4 \pi r^2 R^2$ )against $r$ for an electron in $n p$ orbital of a many electron atom is given below.

The value of $n$ is
2
3
4
5
A buffer solution contains 100 ml of $0.01(\mathrm{M}) \mathrm{CH}_3 \mathrm{COOH}$ and 200 ml of $0.02(\mathrm{M}) \mathrm{CH}_3 \mathrm{COONa}_a .700 \mathrm{ml}$ of water is added subsequently to the buffer solution.The pH before and after dilution are [given,$p K_a=4.74 ; \log 2=0.301$ ]
$5.04,5.04$
$5 \cdot 04,0 \cdot 504$
$5 \cdot 04,1 \cdot 54$
$5 \cdot 34,5 \cdot 34$
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