List of top Questions asked in CBSE Class XI

Fig. 13.18 depicts four x-t plots for linear motion of a particle. Which of the plots represent periodic motion? What is the period of motion (in case of periodic motion) 
Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?
  1. \(PCl_5 (g) ⇋ PCl_3 (g) + Cl_2 (g)\)
  2. \(CaO (s) + CO_2 (g) ⇋ CaCO_3 (s)\)
  3. \(3Fe (s) + 4H_2O (g) ⇋ Fe_3O_4 (s) + 4H_2 (g)\)

The oxygen molecule has a mass of 5.30 × 10-26 kg and a moment of inertia of 1.94 ×10-46 kg m2 about an axis through its centre perpendicular to the lines joining the two atoms. Suppose the mean speed of such a molecule in a gas is 500 m/s and that its kinetic energy of rotation is two thirds of its kinetic energy of translation. Find the average angular velocity of the molecule.

Briefly explain the following statements from the text.
1.“You neither travelled to the past nor the future. You were in the present experiencing a different world.”
2. “You have passed through a fantastic experience: or more correctly, a catastrophic experience.”
3. Gangadharpant could not help comparing the country he knew with what he was witnessing around him.
4. “The lack of determinism in quantum theory!”
5. “You need some interaction to cause a transition.”
The first ionization constant of H2S is 9.1 × 10–8. Calculate the concentration of HS– ion in its 0.1M solution. How will this concentration be affected if the solution is 0.1M in HCl also? If the second dissociation constant of H2S is 1.2 × 10–13, calculate the concentration of S2– under both conditions.
Traditions, rituals and funerary practices must be respected.
In the triangle ABC with vertices A (2, 3), B (4, –1) and C (1, 2), find the equation and length of altitude from the vertex A.

In a test experiment on a model aeroplane in a wind tunnel, the flow speeds on the upper and lower surfaces of the wing are 70 m s–1and 63 m s-1 respectively. What is the lift on the wing if its area is 2.5 m2 ? Take the density of air to be 1.3 kg m–3.

Give reasons for the following.
(i) King Tut’s body has been subjected to repeated scrutiny.
(ii) Howard Carter’s investigation was resented.
(iii) Carter had to chisel away the solidified resins to raise the king’s remains.
(iv) Tut’s body was buried along with gilded treasures.
(v) The boy king changed his name from Tutankhaten to Tutankhamun.
In Class XI of a school 40% of the student's study Mathematics and 30% study Biology. 10% of the class study both Mathematics and Biology. If a student is selected at random from the class, find the probability that he will be studying Mathematics or Biology.
Find the distance between parallel lines
(i) \(15x + 8y – 34 = 0\) and \(15x + 8y + 31 = 0\)
(ii) \(l (x + y) + p = 0\) and \(l (x + y) – r = 0.\)
At 700 K, equilibrium constant for the reaction:
\(H_2 (g) + I_2 (g) ⇋ 2HI (g)\)
is 54.8. If 0.5 mol L–1 of HI(g) is present at equilibrium at 700 K, what are the concentration of H2(g) and I2(g) assuming that we initially started with HI(g) and allowed it to reach equilibrium at 700 K?
Prove that cos 4x =1-8 sin2 x cos2 x
i and j are unit vectors along x- and y- axis respectively. What is the magnitude and direction of the vectors i+j and i-j ? What are the components of a vector A= 2 i + 3 j along the directions of i + j + and i - j ? [You may use graphical method]
Tibetan mastiffs were popular in China’s imperial courts.Give reason.
The ejection of the photoelectron from the silver metal in the photoelectric effect experiment can be stopped by applying the voltage of 0.35 V when the radiation 256.7 nm is used. Calculate the work function for silver metal.
(i) List the deeds that led Ray Johnson to describe Akhenaten as “wacky”.
(ii) What were the results of the CT scan?
(iii) List the advances in technology that have improved forensic analysis.
(iv) Explain the statement, “King Tut is one of the first mummies to be scanned — in death, as in life...”
The author was disappointed with Darchen. Give reason.
The sum of two numbers is 6 times their geometric mean, show that numbers are in the ratio (3+2√2) : (3-2√2).

Reduce  \((\frac{1}{1-4i}-\frac{2}{1+i})(\frac{3-4i}{5+i})\) to the standard form .

Draw a standard ECG and explain the different segments in it.
Have you known someone like the author’s grandmother? Do you feel the same sense of loss with regard to someone whom you have loved and lost?
How does the story suggest that optimism helps to endure “the direst stress”?
Mention the odd way in which the author’s grandmother behaved just before she died.
The first ionization enthalpy values (in kJmol-1 ) of group 13 elements are :
BAlGaInTl
801577579558589
How would you explain this deviation from the general trend?