List of top Chemistry Questions

Thermoplastics become hard on heating and soft on cooling. Thermoplastics are cross-linked polymers which are soluble in many organic solvents.

The normal boiling point of water is $100 \,^{\circ}C$ and standard boiling point of water is $99.6 \,^{\circ}C$. The temperature at which vapour pressure of liquid is equal to the external pressure is called boiling temperature at that pressure.

The monomer of neoprene is $1, 3$-butadiene. Neoprene is highly inflammable.

The melting and boiling points of the alkali metals are low. Alkali metals have weak metallic bonding.

The maximum number of electrons in the shell with principal quantum number $n$ is equal to $2n^{2}$. Two electrons can have the same value of three quantum numbers $n,l$ and $m_{b}$ but must have the opposite spin quantum number.

The maximum oxidation state of chromium in its compounds is $+6$. Chromium has only six electrons in $ns$ and $(n - 1)d$ orbitals.

The gases show ideal behaviour when the volume occupied is large so that the volume of the molecules can be neglected in comparison to it. The behaviour of the gas becomes more ideal when pressure is very low.

The dipole moment in case of $BeF_2$ is zero. The two equal bond dipoles point in opposite directions and cancel the effect of each other.

The characteristics of cathode rays do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube. Cathode rays consist of negatively charged particles, called electrons.

The atomic size generally increases across a period and decreases down the group. Atomic size depends upon valence shell electronic configuration.

Superoxides of alkali metals are paramagnetic. Superoxides contain $O_2^-$ ion which has one unpaired electron.

Soluble fluoride is often added to drinking water to bring its concentration up to $1\, ppm$. $F^{-}$ ion concentration above $2 \,ppm$ causes brown mottling of teeth.

$SiC$ has higher melting point than $NaCl$. $SiC$ has stronger electrostatic forces of attraction.

Quartz glass is crystalline solid and quartz is an amorphous solid. Quartz glass has long range order.

Purine bases present in $DNA$ are adenine and guanine. The base thymine is present in $RNA$ while base uracil is present in $DNA$.

$pK_a$ value of phenol is $10.0$ while that of ethanol is $15.9$ Ethanol is stronger acid than phenol.

$ PHBV$ is a biodegradable polymer. $ PHBV$ is an aliphatic polyester.

Oxidation state of oxygen in $OF_{2}$ and $Na_{2}O$ is $+2$ and $-2$ respectively. Oxygen is an electronegative element.

$O_{2}$ molecule is diamagnetic while $C_{2}$ molecule is paramagnetic in nature. Bond order of $O_ 2$ molecule is $1.5$ and that of $C_2$ molecule is $2.5$.

$Na_{2}O$ is basic oxide whereas $Cl_{2}O_{7}$ is acidic oxide. Elements on extreme left form basic oxides whereas elements on extreme right form acidic oxides.

Lyophilic colloids have a unique property of protecting lyophobic colloids. Lyophilic colloids are extensively solvated.

Lithium salts are mostly hydrated. The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes.

$K_4[Fe(CN)_6]$ is diamagnetic and $[Fe(H_2O)_6 ]Cl_3$ is paramagnetic. Hybridisation of central metal m $K_4[Fe(CN)_6] is \,sp^3d^2,$ while in $[Fe(H_2O)_6]Cl_3\, is\, d^2\, sp^3$

Isocyanide test can be used to distinguish between secondary and tertiary amines. Tertiary amines on heating with chloroform and ale. $KOH$ form foul smelling substances.

In the series $Sc$ to $Zn$, the enthalpy of atomisation of zinc is the lowest. Zinc has greater number of unpaired electrons.