Question

Identify X, Y, and Z based on the following observations.

	X(Fe)	Y(Na)	Z(Mg)
Hardness	Hard	Soft	Relatively soft
Reactivity with water	Reacts with steam	Reacts with cold water	Reacts with hot water
Reaction with $CaC{l}_2$	No reaction	Formation of metal chloride	No reaction
Reaction with $ZnC{l}_2$	No reaction	Formation of metal chloride	Formation of metal chloride

[0.8 mark]

• A. $Fe,Li,Na$
• B. $Al,Na,Pb$
• C. $Fe,Na,Mg$
• D. $Al,Ag,Na$

Answer 1

The correct option is C $Fe,Na,Mg$

The given properties of the elements X, Y, and Z can be interpreted as follows:

A. Hardness:
Iron $\left(Fe\right)$ is hard, sodium $\left(Na\right)$ is soft, and magnesium $\left(Mg\right)$ is relatively soft.

B. Reaction with water:
Iron reacts with only steam to form iron oxide and hydrogen gas.
$3\mathrm{Fe}\left(s\right)+4H_{2}O\left(g\right)\to {\mathrm{Fe}}_3{O}_3\left(s\right)+4H_2\left(g\right)$

Sodium reacts with hot water to form sodium hydroxide and hydrogen gas.
$2\mathrm{Na}\left(s\right)+2H_{2}O\left(l\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)+H_2\left(g\right)$

Magnesium reacts with cold water to form magnesium hydroxide and hydrogen gas.
$\mathrm{Mg}\left(s\right)+2H_{2}O\left(l\right)\to \mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+H_2\left(g\right)$

C. Reaction with $CaC{l}_2$
Iron being less reactive than calcium, shows no reaction with calcium chloride.
$\mathrm{Fe}\left(s\right)+{\mathrm{CaCl}}_2\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

Sodium being more reactive than calcium, displaces calcium to form sodium chloride.
$2\mathrm{Na}\left(s\right)+{\mathrm{CaCl}}_2\left(\mathrm{aq}\right)\to \mathrm{Ca}\left(s\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$

Magnesium being less reactive than calcium, shows no reaction with calcium chloride.

$\mathrm{Mg}\left(s\right)+{\mathrm{CaCl}}_2\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

(d) Reaction with ZnCl2
Iron being less reactive than zinc, shows no reaction with zinc chloride.
$\mathrm{Fe}\left(s\right)+{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

Sodium being more reactive than zinc, displaces zinc to form sodium chloride.
$2\mathrm{Na}\left(s\right)+{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)\to \mathrm{Zn}\left(s\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$

Magnesium being more reactive than zinc, displaces zinc to form magnesium chloride.
$Mg\left(s\right)+ZnC{l}_2\left(aq\right)\to Zn\left(s\right)+MgC{l}_2\left(aq\right)$