The correct option is C unconditional undertaking to pay
According to the Negotiable Instruments Act, 1881, a promissory note is defined as an instrument in writing (not being a bank note or a currency note), containing an unconditional undertaking signed by the maker, to pay a certain sum of money only to or to the order of a certain person, or to the bearer of the instrument. However, according to the Reserve Bank of India Act, a promissory note payable to bearer is illegal. Therefore, a promissory note cannot be made payable to the bearer.