The temperature coefficient of resistance for most of metals in pure form is positive because on increasing temperature of metals, its resistance increases. Hence, statement I is true. In the statement II, Given, diameter of wire =2‌mm ∴ radius, r=1‌mm=10−3m Charge, q=360πC Time, t=2h=2×60×60s=7.2×103s Charge density, n=5×1022 electrons ∕cm3 =5×1028 electrons ∕m3 Current flowing through the wire. I=‌
q
t
=‌
360Ï€
7.2×103
=‌
Ï€
20
A We know that, I=neAvd ⇒vd=‌
I
neA
‌=‌
π∕20
5×1028×1.6×10−19×π×(10−3)2
‌=6.25×10−6m∕s Hence, statement II is also true. Semiconductors like pure germanium are operated in non-linear region, hence these do not obey Ohm's law. Hence, statement III is also true.