Which of the following metals is soft enough to be cut easily with a knife?

Generally,non-metals are not conductors of electricity. Which of the following is a good conductor of electricity?

How is copper obtained from $Cu_{2}S$? Give reactions.

$(i)$ Given below are the steps for the extraction of copper from its ore. Write the reactions involved:
$(a)$ Roasting of copper $(I)$ sulphide
$(b)$ Reduction of copper $(I)$ oxide with copper $(I)$ sulphide
$(c)$ Electrolytic refining
$(ii)$ Draw a neat and well-labelled diagram for the electrolytic refining of copper.

Make the correct pairs from below mentioned $'X'$ and $'Y':$

$1. \text{Sulphurous acid}$	$p. H_{3}PO_{4}$
$2. \text{Sulphuric acid}$	$q. H_{2}S_{2}O_{7}$
$3. \text{Oleum}$	$r. H_{2}SO_{3}$
$4. \text{Phosphoric acid}$	$s. H_{2}SO_{4}$

Why does a magnesium ribbon start floating when it is placed in hot water?