Holme's signal uses calcium carbide and calcium phosphide. The spontaneous combustion of phosphine is technically used in Holme's signals. Containers containing a mixture of calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases burn and serve as a Signal.

Key Idea An oxidising agent is a species, which oxidises the other species and itself gets reduced.
\[\begin{align} & \left( \text{i} \right)C\overset{0}{\mathop{u}}\,+2{{H}_{2}}S{{O}_{4}}\to \overset{+2}{\mathop{Cu}}\,S{{O}_{4}}+S{{O}_{2}}+2{{H}_{2}}O \\ & \left( \text{ii} \right)3\overset{0}{\mathop{S}}\,+2{{H}_{2}}S{{O}_{4}}\to \overset{+4}{\mathop{3S{{O}_{2}}}}\,+2{{H}_{2}}O \\ & \left( \text{iii} \right)\overset{0}{\mathop{C}}\,+{{H}_{2}}S{{O}_{4}}\to \overset{+4}{\mathop{C{{O}_{2}}}}\,+2S{{O}_{2}}+2{{H}_{2}}O \\ & \left( \text{iv} \right)\overset{+2}{\mathop{C}}\,a{{\overset{-1}{\mathop{F}}\,}_{2}}+{{H}_{2}}S{{O}_{4}}\to \overset{+2}{\mathop{Ca}}\,S{{O}_{4}}+2H\overset{-1}{\mathop{F}}\, \\ \end{align}\]
In reaction (iv), oxidation number of elements remains unchanged. Thus, in this reaction, $${H_2}S{O_4}$$  does not act as an oxidising agent.

Chlorine is good oxidising agent than bromine, so, $$C{l_2}$$  oxidise $$B{r^ - }$$  to bromine.
$$2KBr + C{l_2} \to 2KCl + B{r_2}$$

The maximum valency of beryllium is $$ + 2$$  while that of aluminium is $$ + 3$$ .

$$\,HI$$ and $$HBr$$  (in that order) are the strongest reducing hydracids and hence they reduce $${H_2}S{O_4}$$ . $$HCl$$  is quite stable and hence is oxidised by strong oxidising agent like $$KMn{O_4}$$ . $$HF$$  is not a reducing agent. In the smallest $${F^ - }$$ ion, the electron which is to be removed during oxidation is closest to the nucleus and therefore most difficult to be removed. Therefore, $$HF$$  is a poor reducing agent.

$$Al < Ga < In < Tl$$
This is due to inert pair effect or tendency of $$n{s^2}$$ electrons do not participate in bond formation. This tendency decreases on moving down the group.

Carbon dioxide is not a poisonous gas.

$${H_4}{P_2}{O_6}$$  has $$P-P$$  linkage

Glass is an example of amorphous solid. It is also known as supercooled liquid. Glass have short range order of constituents.

$$ICl$$
Order of reactivity of halogens
$$C{l_2} > B{r_2} > {I_2}$$
But, the interhalogen compounds are generally more reactive than halogens $$({\text{expect}}\,{F_2})$$  , since the bond between two dissimilar electronegative elements is weaker than the bond between two similar atoms i.e, $$X - X$$