Question

which sequence of elements is arranged in decreasing order of atomic radii?
a. al, si, p
b. cl, br, i
c. li, na, k
d. n, c, b

Explanation:

Step1: Recall atomic radius trends

Atomic radius decreases across a period (left to right) and increases down a group (top to bottom) in the periodic table.

Step2: Analyze Option A (Al, Si, P)

Al, Si, P are in the same period (period 3), left to right. So atomic radius should decrease: Al > Si > P (decreasing order). Check if this matches.

Step3: Analyze Option B (Cl, Br, I)

Cl, Br, I are in the same group (group 17), top to bottom. Atomic radius increases: Cl < Br < I. So decreasing order would be I > Br > Cl, not Cl > Br > I. Eliminate B.

Step4: Analyze Option C (Li, Na, K)

Li, Na, K are in group 1, top to bottom. Atomic radius increases: Li < Na < K. Decreasing order would be K > Na > Li, not Li > Na > K. Eliminate C.

Step5: Analyze Option D (N, C, B)

N, C, B are in period 2, right to left. Atomic radius increases: N < C < B. Decreasing order would be B > C > N, not N > C > B. Eliminate D.

Answer:

A. Al, Si, P