All of the following statements concerning voltaic cells are true except

1) oxidation occurs at the cathode.
2) a salt bridge allows cations and anions to move between the half-cells.
3) electrons flow from the anode to the cathode in the external circuit.
4) a voltaic cell can be used as a source of energy.
5) a voltaic cell consists of two-half cells.

In a voltaic cell, oxidation does not occur at the cathode.

A voltaic cell is an electrochemical cell that converts chemical energy to electrical energy, hence it can be used as a source of energy.  It consists of two separate half-cells. There is a salt bridge between the two half cells allowing for the  free flow of ions from one cell to another.

There are two electrodes, the anode undergoes oxidation and the cathode undergoes reduction. Electrons flow from the anode to the cathode.

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oxidation occurs at the cathode.

Explanation:

In a voltaic cell electrons move from anode to cathode. At the anode, species give up electrons. This is an oxidation reaction depicted by the oxidation half equation. At the cathode, species accept electrons and become reduced. This is depicted by the reduction half equation. In summary; in a Voltaic cell, oxidation occurs at the anode while reduction occurs at the cathode.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms