Which of the following processes is reversible

$U\,\,\, 1s^2 \,2s^2 \,2p^3$
$V\,\,\, 1s^2\,2s^2 \,2p^6 \,3s^1$
$W\,\,\, 1s^2\,2s^2\, 2p^6\,3s^2\,3p^2$
$X\,\,\, 1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^5\, 4s^2$
$Y\,\,\, 1s^2\, 2s^2\,2p^6\,3s^2\,3p^6\,3d^{10}\, 4s^2\, 4p^6$

Determine which sequence of elements satisfy the following statements :
$(i)$ Element forms a carbonate which is not decomposed by heating
$(ii)$ Element is most likely to form coloured ionic compounds
$(iii)$ Element has largest atomic radius
$(iv)$ Element forms only acidic oxide

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The value of $\Delta H$ for the reaction $X_{2(g)} + 4Y_{2(g)} \rightleftharpoons XY_{4(g)}$ is less than zero. Formation of $XY_{4(g)}$ will be favoured at

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The Henry's law constant $\left(\mathrm{K}_H\right)$ values of three gases $(A, B, C)$ in water are $145,2 \times 10^{-5}$ and $35$ kbar, respectively. The solubility of these gases in water follow the order:

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Which orbital is dumb-bell shaped ?

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$A, B$ and $C$ are hydroxy-compounds of the elements $X, Y$ and $Z$ respectively. $X ,Y$ and $Z$ are in the same period of the periodic table. $A$ gives an aqueous solution of $pH$ less than seven. $B$ reacts with both strong acids and strong alkalis. $C$ gives an aqueous sohuion which is strongly alkaline.
Which of the following statements is / are true ?

$I :$ The three elements are metals.

$II :$ The electro negativities decrease from $X$ to $Y$ to $Z$.

$III :$ The atomic radius decreases in the order $X, Y$ and $Z.$

$IV : X, Y$ and $Z$ could be phosphorus, aluminium and sodium respectively.