Why is an ammeter likely to be burnt if you connect it in parallel?

$(a)$ Name an instrument that measures electric current in a circuit. Define the unit of electric current.
$(b)$ What do the following symbols mean in circuit diagrams?
$(c)$ An electric circuit consisting of a $0.5 \ m$ long nichrome wire $XY$,an ammeter,a voltmeter,four cells of $1.5 \ V$ each and a plug key was set up.
$(i)$ Draw a diagram of this electric circuit to study the relation between the potential difference maintained between the points $X$ and $Y$ and the electric current flowing through $XY$.
$(ii)$ The following graph was plotted between $V$ and $I$ values. What would be the values of $V/I$ ratios when the potential difference is $0.8 \ V$,$1.2 \ V$ and $1.6 \ V$ respectively? What conclusion do you draw from these values?

How is a voltmeter connected in a circuit?

Define electric current and state its $SI$ unit. With the help of $Ohm's$ law,explain the meaning of $1$ ohm resistance.

How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?

$A$ cylinder of a material is $10\, cm$ long and has a cross-section of $2\, cm^{2}$. If its resistance along the length is $20\, \Omega$,what will be its resistivity in number and units?