Question
Give reasons:
Lakes freeze from top towards bottom.
Lakes freeze from top towards bottom.
✓
Answer
During severe winter, the temperature of water in the lake keeps on decreasing. Since cold water is heavier, it keeps on going into the interior of the lake while warm water keeps on coming to the surface of the lake. This process continues till the temperature of entire water of lakes becomes 4°C. Since density of water is maximum at 277K, any further decrease in the temperature will decrease its density. As a result, the temperature of the surface water keeps on decreasing and it ultimately freezes. Now, any further decrease in the temperature will decrease the temperature of water below 4°C. This process continues and as a result, the lakes keep on freezing from top to bottom.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
Explain the following: (i) Markownikov's Law (ii) Peroxide effect
What is resonance? Also explain its rules.
Calculate the molarity of a solution of ethanol in water, in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).
Pay load is defined as the difference between the mass of displaced air and the mass of the balloon. Calculate the pay load when a balloon of radius $10 \ m$ , mass $100 \ kg$ is filled with helium at 1.66 bar at $27^{\circ} C$. (Density of air $=1.2 kg$ $m ^{-3}$ and $R =0.083 bar dm ^3 K^{-1} mol^{-1}$ ).
→|
S. No
|
Column I
|
Column II
|
|
1.
|
$[Mn(CO)_5]^-$
|
+6
|
|
2.
|
$[Mn_2(CO)_{10}]$
|
+2
|
|
3.
|
$K_4[Mn(CN)_6]$
|
0
|
|
4.
|
$K_2MnO_4$
|
-1
|
Give general characters of elements of s, p, d and f-block.
Match the correct atomic radius with the element.
|
Element
|
|
Atomic radius
|
|
|
i.
|
Be
|
A.
|
74
|
|
ii.
|
C
|
B.
|
88
|
|
iii.
|
O
|
C.
|
111
|
|
iv.
|
B
|
D.
|
77
|
|
v.
|
N
|
E.
|
66
|
What will be the work done on an ideal gas enclosed in a cylinder, when it is compressed by a constant external pressure, $p_{ext}$ in a single step as shown in Fig. Explain graphically.
→1. Suggest a method to purify
i. a liquid which decomposes at its boiling point.
ii. kerosene oil containing water.
iii. camphor containing traces of common salt.
2. Giving justification, categorise the following molecules/ions as nucleophile or electrophile:
$
\begin{aligned}
& HS^{-}, BF_3, C_2 H_5 O^{-},\left(CH_3\right)_3 N:, \\
& C \stackrel{+}{l}, C H_3-\stackrel{+}{C}=O, H_2 N \stackrel{+}{:}, \stackrel{+}{N} O_2
\end{aligned}
$
→i. a liquid which decomposes at its boiling point.
ii. kerosene oil containing water.
iii. camphor containing traces of common salt.
2. Giving justification, categorise the following molecules/ions as nucleophile or electrophile:
$
\begin{aligned}
& HS^{-}, BF_3, C_2 H_5 O^{-},\left(CH_3\right)_3 N:, \\
& C \stackrel{+}{l}, C H_3-\stackrel{+}{C}=O, H_2 N \stackrel{+}{:}, \stackrel{+}{N} O_2
\end{aligned}
$
Although both $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}$ are triatomic molecules, the shape of $\mathrm{H}_2 \mathrm{O}$ molecule is bent while that of $\mathrm{CO}_2$ is linear. Explain this on the basis of dipole moment.
→