Silver (atomic weight = $108 \mathrm{g} {\mathrm{mol}}^{-1}$ ) has a density of $10.5 \mathrm{g} {\mathrm{cm}}^{-3}$. The number of silver atoms on a surface of area ${10}^{-12} {\mathrm{m}}^2$ can be expressed in scientific notation as $\mathrm{y}\times {10}^{\mathrm{x}}$. The value of x is

Among the following, the number of elements showing only one non-zero oxidation state is

$\mathrm{O}, \mathrm{Cl}, \mathrm{F}, \mathrm{N}, \mathrm{P}, \mathrm{Sn}, \mathrm{Tl}, \mathrm{Na}, \mathrm{Ti}$.

The ammonia prepared by treating ammonium sulphate with calcium hydroxide is completely used by ${\mathrm{NiCl}}_2.6{\mathrm{H}}_2\mathrm{O}$ to form a stable coordination compound. Assume that both the reactions are $100 \%$ complete. If $1584 \mathrm{g}$ of ammonium sulphate and $952 \mathrm{g}$ of ${\mathrm{NiCl}}_2.6{\mathrm{H}}_2\mathrm{O}$ are used in the preparation, the combined weight (in grams) of gypsum and the nickel-ammonia coordination compound thus produced is _____. (Atomic weights in $\mathrm{g} {\mathrm{mol}}^{-1}$: $\mathrm{H} = 1, \mathrm{N} = 14, \mathrm{O} = 16, \mathrm{S} = 32, \mathrm{Cl}= 35·5, \mathrm{Ca}= 40, \mathrm{Ni}= 59$)