The mass spectrometer can be used to measure mass of

A. an atom

B. an electron

C. a proton

D. a neutron

Find the number of neutrons in an atom represented by 45₂₁X.

A. 21

B. 24

C. 45

D. 66

The valence electrons in a chloride ion are [₁₇CI]

A. 2p electrons only

B. 3s and 3p electrons only

C. 3p and 3d electrons only

D. 3p electrons only

What is the atomic number of an element whose cation Y⁺ has the electronic configuration 1s²2s²2p⁶?

A. 9

B. 10

C. 11

D. 12

Atom \(^{234} _{88} Q\) decay by alpha emission to give an atom R. The atomic number and mass number of atom R are respectively

A. 86 and 230

B. 87 and 234

C. 88 and 233

D. 90 and 238

Which of the following statements is not true of halogens?

A. they exist in different physical states

B. they exist as diatomic molecules

C. their ionic radii decrease down the group

D. their melting and bolling points increase down the group

Elements in the same group of the periodic table have

A. the same number of valence electrons

B. the same number of electron shells

C. different chemical behaviour

D. the same atomic size

Consider the following elements and their electronic configurations
W: 1s²2s²
X: 1s ²2s²2p⁶
Y: 1s²2s²2p⁶3s²
Z: 1s²2s²2p⁶3s²3p². Which of t

A. W and X only

B. Y and Z only

C. W and Y only

D. W, Y and Z only

Arrange the following elements in order of increasing electron affinity: Br₂CI₂
I ₂
F ₂

A. I ₂CI₂Br₂F ₂

B. I ₂Br₂CI₂F ₂

C. CI₂ I ₂Br₂F ₂

D. Br₂CI₂ I ₂ F ₂