Carbon has __________ isotopes.

Assertion : from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells.

Reason : The energetics b-particles emitted in the decay of damage the bone marrow.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(d) If the assertion and reason both are false.

→

A heavy nucleus at rest breaks into two fragments which fly off with velocities in the ratio 8 : 1. The ratio of radii of the fragments is

(a) 1 : 2

(b) 1 : 4

(d) 2 : 1

→

The shows two NAND gates followed by a NOR gate. The system is equivalent to the following logic gate

Two wires A and B are made of same material. The wore A has a length l and diameter r while the wire B has a length 2l and diameter $\frac{\text{r}}{2}$. If the two wires are stretched by the same force, the elongation in A divided by the elongation in 8 is:

$\frac{1}{8}$
$\frac{1}{4}$
$4$
$8$

→

Carbon -14 decays with half-life of about 5,800 years. In a sample of bone, the ratio of carbon -14 to carbon -12 is found to be of what it is in free air. This bone may belong to a period about x centuries ago, where x is nearest to