Assertion
A pure semiconductor has negative temperature coefficient of resistance.
Reason
In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.
(A) Assertion is true, Reason is true; Reason is a correct explanation for Assertion
(B) Assertion is true, Reason is true; Reason is not a correct explanation for Assertion
(C) Assertion is true, Reason is false
(D) Assertion is false, Reason is true

Hint:
Initially you must read the assertion and answer carefully. A semiconductor is material which has a conductivity between conductors and insulators. Electrons on heating a semiconductor are burst inside the material very efficiently.

Complete step by step solution:
Semiconductor, any of a category of crystalline solids intermediate in electrical conductivity between a conductor and an insulator. Semiconductors are employed within the manufacture of varied forms of electronic devices, including diodes, transistors, and integrated circuits. Such devices have found wide application due to their compactness, reliability, power efficiency, and low cost.
As discrete components, they need found use in power devices, optical sensors, and light-weight emitters, including solid-state lasers.
When the temperature is raised, a number of the covalent bonds within the semiconductor break thanks to the thermal energy supplied.
 The breaking of the bond set those electrons free which are engaged within the formation of those bonds.
In semiconductors, by increasing temperature, bond breaks and conduction holes and electrons increase.

So, option A is the correct option.

Note:
Examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the table. After silicon, gallium arsenide is the second commonest semiconductor and is employed in laser diodes, solar cells, microwave-frequency integrated circuits etc.
Semiconductor materials are nominally small band gap insulators.