Correct Option: B

All the loops have equal areas. B at any distance r from the wire is k/ r. For any rectangular loop of height h (in the direction of the wire) and width w (⊥ the wire), the flux φ is

	a + w	khdr	∞	= kh ln	a + w
	a	r			a

where a is the distance of the near side from the wire.
Thus,

for 1, φ1 = k l ln	a + 1
	a

for 2, φ2 = k 2l ln	a + 1/2
	a

for 3, φ3 =	1	k2l ln	a + 1/4 + 1
	2		a + 1/4

for 4, φ4 =	kl ln	a + 2 l
		a

φ1 = kl ln		1 +	1		,φ2 = 2kl ln		1 +	1
			a					a

φ3 = kl ln

1 +

1

,φ4 =

1

kl ln

1 +

2 l

a + 1/4

2

a

The long terms do not change by significant amount. Thus, φ₂ should be of highest value.
Hence alternative (B) is the correct choice.