Elements — W, X, Y & Z have electronic configurations:
W = 2,8,1
X = 2,8,7
Y = 2,5
Z = 1

(i) What type of bond is formed between:
    (a) W and X
    (b) Y and Z

(ii) What is the formula of the compound formed between :
    (a) X and Z
    (b) W and X

(i) Type of bond formed

(a) W (2,8,1) and X (2,8,7) — Electrovalent bond is formed as W donates 1 electron and X takes up that electron and both attain a stable octet.

(b) Y (2, 5) and Z (1) — Covalent bond as electron sharing takes place between the two elements. The valency of Z element is 1 and that of Y is 3. Z needs one electrons to attain stable duplet structure of nearest noble gas - He [2] and Y needs three electrons to attain stable octet structure of nearest noble gas - Ne [2,8]
One Y atom shares three electron pairs one with each of the three atoms of Z such that Z acquires a duplet configuration and Y attain a stable octet configuration resulting in the formation of three single covalent bonds.

(ii) Formula of the compound formed

(a) X (2,8,7) and Z (1) — XZ as X needs one 1 electron to complete it's octet and Z needs needs one electron to complete it's duplet hence, they both share one electron pair and forms ZX compound.

(b) W (2,8,1) and X (2,8,7) — WX as W has the tendency to donate one electron and gain stability whereas X has the tendency to gain one electron to be stable. Hence, W donates one electron and X takes it and form WX compound.