List of top Questions asked in CBSE Class XI

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

\(2AgBr (s) + C_6H_6O_2(aq) \rightarrow 2Ag(s) + 2HBr (aq) + C_6H_4O_2(aq)\)
\(HCHO(l) + 2[Ag (NH_3)_2] ^+ (aq) + 3OH^ - (aq) \rightarrow 2Ag(s) + HCOO ^- (aq) + 4NH_3(aq) + 2H_2O(l)\)
\(HCHO (l) + 2Cu^{ 2+}(aq) + 5 OH^ - (aq) \rightarrow Cu_2O(s) + HCOO ^- (aq) + 3H_2O(l)\)
\(N_2H_4(l) + 2H_2O_2(l) \rightarrow N_2(g) + 4H_2O(l)\)
\(Pb(s) + PbO_2(s) + 2H_2SO_4(aq) \rightarrow 2PbSO_4(s) + 2H_2O(l)\)

Figure 8.9 shows the strain-stress curve for a given material. What are (a) Young’s modulus and (b) approximate yield strength for this material?

strain-stress curve for a given material

Arrange the bonds in order of increasing ionic character in the molecules: LiF, K₂O, N₂, SO₂and ClF₃.

Three reasons why the author’s grandmother was disturbed when he started going to the city school.

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed V. If the collision is elastic, which of the following (Fig. 5.14) is a possible result after collision ?

Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

Prove that, cos ⁶x = 32cos⁶x-48cos⁴ x+18cos²x -1.

\(\text{tan x}=-\frac{4}{3},\text{x\, in\, quadrant \,II.}\)

If the function f(x) satisfies \(\lim_{x\rightarrow 1}\) \(\frac{f(x)-2}{x^2-1}\) =\(\pi\), evaluate \(\lim_{x\rightarrow 1}\) f(x).

\(∆U^Θ\) of combustion of methane is – \(X\ kJ \ mol^{–1}\). The value of \(∆H^Θ\) is

Write the resonance structures for SO₃, NO₂ and NO₃^-

Briefly comment on "The purpose of the author’s journey to Mount Kailash."

Given the standard electrode potentials,
K⁺ /K = -2.93V,
Ag⁺/Ag = 0.80V,
Hg²⁺/Hg = 0.79V
Mg²⁺/Mg = -2.37V.
Cr³⁺/Cr = -0.74V
Arrange these metals in their increasing order of reducing power.

An aircraft is flying at a height of 3400 m above the ground. If the angle subtended at a ground observation point by the aircraft positions 10.0 s a part is 30°, what is the speed of the aircraft ?

Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.

Assign oxidation numbers to the underlined elements in each of the following species:

\(NaH_2\underline PO_4\)
\(NaH\underline SO_4\)
\(H_4\underline P_2O_7\)
\(K_2\underline {Mn}O_4\)
\(Ca\underline O_2\)
\(Na\underline BH_4\)
\(H_2\underline S_2O_7\)
\(KAl(\underline SO_4)_2.12 H_2O\)

If \(\frac{ a + bx }{ a - bx }= \frac{b + cx }{ b - cx} =\frac{ c + dx }{ c - dx }(x ≠ 0),\) then show that a, b, c and d are in G.P.

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 reaction CH₃CH₂I + KOH(aq) \(\rightarrow\) CH₃CH₂OH + KI is classified as

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.

Draw the Lewis structures for the following molecules and ions: \(H_2S\), \(SiCl_4\), \(BeF_2\), \(CO_3^{2-}\) , \(HCOOH\)

The following results are observed when sodium metal is irradiated with different wavelengths. Calculate (a) threshold wavelength and, (b) Planck’s constant

λ (nm)	500	450	400
v × 10^–5(cm s^–1)	2.55	4.35	5.35

Prove that. \(2sin^2 \frac{π}{6}+cosec^2 \frac{7π}{6}–cos^2 \frac{π}{3}=\frac{3}{2}\)

Prove that sin x+sin 3x+sin 5x+sin 7x=4 cos x cos 2x sin 4x.

Mention the three phases of the author’s relationship with his grandmother before he left the country to study abroad.