Ravi took four different materials in four different test tubes labelled as P, Q, R and S as shown below.

He added 5 mL dilute hydrochloric acid in each test tube and brought a burning matchstick at the mouth of each test tube. In which case(s), he will hear the pop sound ?

P and Q  are the metals react with acids it produce salt and hydrogen gas.

Mg & Al are more active than Hydrogen.  So they displaces Hydrogen from HCl solution & liberates ${\text{H}}_{\text{2}}$  gas which gives pop sound with burning match stick.

$\text{Mg+2HCl}\to {\text{MgCl}}_2+{\text{H}}_{\text{2}}\left(g\right)$

$2\text{A}l+6\text{HC}l\to 2\text{A}l\text{C}{l}_3+3{\text{H}}_{\text{2}}\left(g\right)$

$\text{Cu}+\text{HC}l\to$ No reaction.

Copper is less reactive than hydrogen.

In test (S) we have charcoal powder which is contains carbon (non-metal).