Question

According to the Lewis acid- base concept:
A.Species in which the central atom has completed octet cannot act as an acid
B.Negatively charged ions are acids
C.The molecule in which a central atom has vacant d-orbitals available acts as an acid
D.All positively charged ions

Answer 1

To answer this question, you should recall the concept of different bases of theory on which acid and base are classified. Electron donors are called Lewis bases while electron acceptors are called Lewis acids.

Complete step by step answer:
Lewis acids and bases are described by the Lewis theory of acid-base reactions as electron-pair acceptors and electron pair donors respectively. Therefore, a Lewis base can donate a pair of electrons to a Lewis acid to form a product containing a coordinate covalent bond. This product is also referred to as a Lewis adduct. Lewis Acids are the chemical species which have empty orbitals and can accept electron pairs from Lewis bases. These chemical species can donate an electron pair to a given Lewis acid to form an adduct.

Hence, option C is correct.

Note:
Make sure you remember the difference between different types of bases and acids.
Arrhenius Acid: Hydronium breaks up to yield a hydronium in solution. Arrhenius Base: Hydroxide is dissolved in water as $O{H^ - }$.
Bronsted-Lowry Acid: Hydronium is a ${H^ + }$donor regardless of the solution. Bronsted-Lowry Base: Hydroxide attacks and accepts the ${H^ + }$ from hydronium.
Lewis Acid: The ${H^ + }$ on Hydronium accepts the attacking electron pair to form a bond. Lewis Base: Hydroxide donates electron pairs present over it to form a bond between itself and ${H^ + }$.