The sky appears dark to passengers flying at very high altitudes mainly because :

A cylindrical conductor of length ‘l’ and uniform are a of cross section 'A' has resistance 'R'. The are a of cross section of another conductor of same material and same resistance but of length '2l’ is

The maximum resistance which can be made using four resistors each of resistance 1/2Ω is

An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be

A. Group 1 and Period 3

B. Group 2 and Period 3

C. Group 13 and Period 8

D. Group 16 and Period 3

OR

Consider the following statements about an element ‘X’ with number of protons 13.

(A) It forms amphoteric oxide

(B) Its valency is three

(C) The formula of its chloride in XCl₃

The correct statements(a) is/are

A. only (A) B. only (B)

C. (A) and (c) D. (A),(B) and (C)

An aqueous solution 'A' turns phenolphthalein solution pink. On addition of an aqueous solution 'B' to 'A, the pink colour disappears. The following statement is true for solution 'A' and 'B'.