What is meant by $1$ ohm resistance?

Write the $SI$ unit of resistivity.

An electric iron has a rating of $750\, W; 200\, V$. Calculate:
$(i)$ The current required.
$(ii)$ The resistance of its heating element.
$(iii)$ Energy consumed by the iron in $2$ hours.

$A$ nichrome wire has a resistance of $10\, \Omega$. Find the resistance of another nichrome wire,whose length is three times and area of cross-section four times the first wire.

If resistors are connected in series,the current through each resistor remains the same.

$(a)$ $A$ Nichrome wire of length $L$ and radius $r$ has a resistance of $10 \, \Omega$. How would the resistance of the wire change when:
$(i)$ only the length of the wire is doubled?
$(ii)$ only the diameter of the wire is doubled? Justify your answer.
$(b)$ Why are the elements of electrical heating devices made up of alloys?