MPF is money market fund whereby they put into normal / fixed deposit, earning more or less the same as retail FD promo rate, but definitely higher than <1y FD board rate.

IPF is bond fund hence mgmt fee is higher, distribution also has to follow income received from bond coupon payment, tends to be more volatile compared to MM fund as it follows bond yield movements. Potentially earning higher return (>6%) eg in 2019.

2c sharing

If everyone choose to withdraw, the cash in the fund will reduce by 1.00 (0.01 x 100 units). Asset becomes 99, unit in circulation remains at 100 (no redemption), assuming no liability / management fee, then the NAV is 99 / 100 = 0.99.