Which one out of the following materials is \(\textit{not}\) paramagnetic
The center of a disk of radius $ r $ and mass $ m $ is attached to a spring of spring constant $ k $, inside a ring of radius $ R>r $ as shown in the figure. The other end of the spring is attached on the periphery of the ring. Both the ring and the disk are in the same vertical plane. The disk can only roll along the inside periphery of the ring, without slipping. The spring can only be stretched or compressed along the periphery of the ring, following Hooke’s law. In equilibrium, the disk is at the bottom of the ring. Assuming small displacement of the disc, the time period of oscillation of center of mass of the disk is written as $ T = \frac{2\pi}{\omega} $. The correct expression for $ \omega $ is ( $ g $ is the acceleration due to gravity): 
Let $ a_0, a_1, ..., a_{23} $ be real numbers such that $$ \left(1 + \frac{2}{5}x \right)^{23} = \sum_{i=0}^{23} a_i x^i $$ for every real number $ x $. Let $ a_r $ be the largest among the numbers $ a_j $ for $ 0 \leq j \leq 23 $. Then the value of $ r $ is ________.
Magnetic material is one that can repel or attract other materials. The process of attraction or repulsion of these materials depends on the arrangement of electrons, which is known as the magnetic moment of that material.
Diamagnetic - With regard to the susceptibility χ, a material is diamagnetic if χ is negative. These materials produce negative magnetization when they are placed in the magnetic field. When placed in a magnetic field, these diamagnetic materials are barely magnetized. Diamagnetic substances are the ones that are repelled by magnets.
Paramagnetic - In the presence of an external magnetic field, the substances that get weakly magnetized are known as paramagnetic substances. The magnetic dipoles align along the direction of the applied field, reinforcing and enhancing the magnetic field. These substances get weakly attracted to a magnet as they tend to move from a weaker magnetic field to a stronger one. The magnetization (M) of paramagnetic materials, discovered by Madam Curie, depends on the temperature (T) and the external magnetic field B.
M = C x (B/T)
Where M = Magnetization
C = Curie Constant
B = External magnetic field
T = Temperature
Ferromagnetic - The materials strongly attracted by the magnetic field are known as ferromagnetic materials.